Sourdough Peanut Butter Blondies

If peanut butter is a whole food group in your house like it is in mine, you need these Sourdough Peanut Butter Blondies. They’re thick, chewy, loaded with peanut butter, and stuffed with chunks of Reese’s peanut butter cups. Finished with silky chocolate ganache and a peanut butter swirl, they’re the perfect fudgy dessert for chocolate peanut butter lovers.

Why You’ll Love This Recipe

Loaded with peanut butter: This blondie has peanut butter in the batter and swirled on top for maximum flavor.
Perfectly chewy: Soft, fudgy centers make these blondies the texture we love.
Uses up discard: Have discard to use? This recipe is the perfect way to put it to work, with an overnight option for added fermentation.
Great to prep ahead: This recipe can be made same day or chilled overnight to fit your schedule.
Guaranteed crowd favorite: Chocolate and peanut butter is a combo no one can skip.

Tools You’ll Need:

9×9-inch baking pan- to bake your blondies. I love this pan 9×9 pan from USA Bakeware.
Parchment paper- to line your pan for easy removal.
Mixing bowls- to mix the blondie batter, chocolate ganache, and peanut butter drizzle.
Whisk- to mix ingredients.
Spatula- to spread the the batter.
Digital kitchen scale (optional)– for accurate measuring, especially helpful with sourdough baking. I linked the one I like here.
Measuring cups and spoons– for measuring ingredients.
Oven safe metal clips (optional)- for holding the parchment down to the pan. I love these metal clips that are heat safe and keep my parchment from sliding around.
Ziplock or pastry bag (optional)- for the peanut butter drizzle.
Toothpick or skewer- for the peanut butter swirl design.

Gather Your Ingredients:

Sourdough discard– Adds flavor and moisture and is the magic that ferments your blondie batter if you want to. Can be used fed, past peak, or straight from the fridge. I also have a swap listed on the recipe card.
Creamy Peanut Butter- You’ll want to make sure you use creamy peanut butter here, Jif or Skippy are great I used the Skippy Natural option. If you swap for a different type of peanut butter, the blondies will be delicious it just may affect the texture.
All-purpose flour– Provides structure to the blondies.
Unsalted Butter– Adds that classic chew to the blondies and used to thin the ganache and peanut butter drizzle.
White Granulated Sugar- Sweetens the blondie and gives that chewy texture and crackly top.
Brown Sugar- adds molasses flavor and chewiness to the blondie.
Eggs + egg yolks- Helps the blondie bind and is the rising agent.
Cornstarch (optional)- adds chewiness to the blondie for that classic fudgy texture. This is optional you can skip it if you’d like!
Vanilla extract– Adds warm cozy flavor to the blondie.
Sea Salt– Balances out the sweetness.
Semi-sweet chocolate chips- used to make the chocolate ganache.
Heavy Cream- thins out the ganache to make it smooth and creamy.
Reese’s cups (optional)- I like using the Reese’s snack sized cups and chopping them up, but you can also use minis or skip them and replace with chocolate chips or peanut butter chips.
Flaky Sea Salt (optional) – I love adding Maldon sea salt flakes on top of my blondies for that extra flair. If you haven’t tried this, I highly suggest it! You can find it link here.

nstructions

Step 1: Mix the Batter

Preheat your oven to 350°F (175°C). Line a 9×9 metal pan with parchment paper, leaving some overhang so the blondies are easy to lift out after chilling. I like to use metal clips to hold my parchment in place. Lightly spray with cooking oil.

In a medium saucepan or microwave-safe bowl, melt the butter and peanut butter until just melted. Whisk until smooth and creamy.

Whisk in the granulated sugar, brown sugar, sourdough discard, eggs, egg yolk, and vanilla extract until the blondie batter is shiny and smooth.

Add the flour, cornstarch, and salt to the blondie batter, and mix just until no streaks remain. Try not to overmix at this point or the blondies will be tough. You just want the flour incorporated.

Sourdough Discard Swap Option: If you don’t have sourdough discard, add the extra flour and milk at this time and mix it into the blondie batter.

Whisk the peanut butter and melted butter until smooth

Chop up 9 of the snack size Reese’s cups up into large chunks (don’t make them too small or they’ll melt into the blondie).

Layer half of the blondie batter into the prepared pan, spreading the batter to the edges of the pan.

Sprinkle the chopped Reese’s over the top of the blondie batter evenly.

Scoop the remaining blondie batter on top of the Reese’s layer, and gently spread the batter to cover the Reese’s to the edges of the pan. If they aren’t entirely covered that’s perfectly fine.

Layer half the blondie batter in the pan

Overnight Fermentation Option: If you want to ferment this brownie batter, cover with plastic and refrigerate overnight in the pan. When you’re ready to bake your brownie, allow to rest at room temperature for about an hour to warm up then bake as instructed.

Step 2: Bake the BLondies

Transfer the blondies to the hot oven, and bake at 350°F for 30-35 minutes, or until the edges are set, the center no longer jiggles, and a toothpick inserted in the center comes out with a little wet batter

Do not bake until the toothpick comes out completely clean. These blondies are meant to be fudgy and will continue to set as they cool. Baking time my vary on your oven, my brownies are done anywhere between 30-35 minutes. If you overbake these, they’ll get bready and ruin the texture.

Cool the blondies completely in the pan before frosting.

For the cleanest blondie texture, you can refrigerate the cooled brownie for 30–60 minutes before frosting.

Step 3: Frost the Blondies

While the blondie cools, prepare the chocolate frosting.

In a microwave safe bowl, heat the cream in the microwave or a small pot until steaming.

In another heat safe bowl, add the chocolate chips, butter, vanilla, and salt.

Pour the hot cream over the chocolate chip mixture, and cover for five minutes.

After the frosting has rested, stir with a whisk until it’s smooth, creamy, and glossy. If the chocolate hasn’t fully melted microwave for 15 second intervals and stir until the frosting is smooth.

Whisk the ganache until silky and smooth

Once the blondies are completely cooled, pour the ganache on top of the brownies and spread it evenly over the brownies to the edge.

In a small bowl, add the peanut butter and butter. Microwave for 30 seconds, and whisk until smooth and runny.

Transfer the peanut butter mixture to a Ziplock or pastry bag, and snip off 1/8 inch off of the end.

Pipe even lines about 1 inch apart diagonally across the chocolate ganache. Using a toothpick or skewer, draw lines in a zig zag motion vertically the opposite direction to create the peanut butter swirl effect.

Spread the ganache on top of the blondie

Top the blondies with 3 more chopped Reese’s cups scattered about and flaky sea salt if desired.

Transfer the pan to the refrigerator and chill for at least 2 hours, or until the frosting is set. I prefer to allow the brownie to chill overnight for it to set up cleanly and for the easiest cuts.

Condensation Note: If you chill the blondies overnight, make sure to cover them with plastic. Typically condensation can form on the top of the frosting if you don’t cover the pan. The condensation should stick to the plastic wrap overnight, and you can remove the plastic as soon as you remove the brownies from the refrigerator.

After the blondies have set up, remove from the refrigerator.

Use the parchment paper to lift the blondies out of the pan. Slice the blondies in thirds both ways, to create 9 bars (or you can cut 12 for smaller sizes).

For the cleanest cuts, wipe the knife with a hot wet paper towel between slices. Enjoy!

Yields 9 blondies or 12 smaller blondies

How to Store:

Room Temperature- Store in an airtight container up to 3 days. Be careful about these blondies sitting in a warm environment, the frosting can melt.

Refrigerator- Keeps up to 5 days in an airtight container in the refrigerator. For the best texture, let them sit at room temperature for 10–15 minutes before serving.

Freezer- You can freeze the unfrosted blondies by wrapping them tightly and freezing for up to 2 months. Thaw in the refrigerator overnight, then frost as directed. Chill and enjoy!

FAQ’S

Can I make these without sourdough discard?

Yes, replace the 1/2 cup (120g) discard with 1/4 cup (60g) milk and 1/4 cup (30g) all-purpose flour.

Why did my blondies turn out dry?

They were likely overbaked. For fudgy blondies, the toothpick should come out with moist, not completely clean.

Can I use natural peanut butter?

I recommend using regular creamy peanut butter for the best texture and consistency. Natural peanut butter can make the blondies oily and less predictable.

If you loved this recipe, drop a comment and leave a star review and don’t forget to checkout more of my sourdough dessert bar recipes!

Sourdough Dessert Bars: