Before you get started on mixing your dough, you'll make your tangzhong. Whisk milk and flour together in a small saucepan.

Cook the tangzhong over medium/low heat, stirring constantly, until it thickens into a paste that is similar to pudding (about 2–3 minutes). For precision, use your digital thermometer and heat to 148-155 F. Do not overheat, or your mixture will be too thick.

Scrape into a bowl immediately to prevent further cooking, cover, and let cool to room temperature before adding to your dough.

In a large bowl or stand mixer bowl, add the tangzhong, sourdough discard, lemon zest, egg, egg yolk, whole milk, white sugar, instant dry yeast, and vanilla. Whisk all the wet ingredients until smooth.

Add the flour and salt to the wet ingredients, and transfer to the stand mixer and knead on Speed 1 or knead by hand for about 3-4 minutes until the dough comes together.

Once the dough has come together, add the softened butter slowly by the Tablespoon. Once you've mixed in a Tablespoon, add another until all of the butter has been worked into the dough.

Mix the butter into the dough with the stand mixer set to Speed 1, or you can do this by kneading the butter in slowly by hand. The dough should me smooth and slightly sticky.

Spray a clean mixing bowl large enough for the dough to double in size with cooking spray, and transfer the dough to the bowl covering it with a lint-free kitchen towel or lid. Allow the dough to rest 20 minutes.

After the 20 minute rest, knead the dough by hand for a minute or two to get the dough even softer and to work the gluten. Once you've finished this kneading step, cover the bowl again.

Allow the dough to rest about 1 1/2 hours at room temperature and the dough is ~75–90% risen. You don't want this dough to proof double fully at this rising point.

If the dough proofs sooner than the time I mentioned, shape it. You want to watch the dough to make sure it doesn't overproof at this stage!

Add the blueberries, sugar, lemon juice, lemon zest, and salt to a small saucepan or pot.

Cook the berry mixture over medium heat, bringing the berries to a simmer or low boil stirring often with a spatula to avoid burning.

Reduce the heat to medium-low and cook for roughly 10 minutes, stirring frequently, until the berries release their juices and begin to break down.

In a small bowl, mix the cornstarch and water to make a slurry.

Stir the slurry into the blueberry mixture and cook for 1 more minute until the berries are thick, glossy, and jammy.

Remove from heat and scrape into a bowl and let the compote cool completely before using. Place a piece of plastic directly on the top of the compote after it cools slightly to avoid a skin forming while you cool it.

Lightly grease a 9×5-inch loaf pan, and fit it with parchment paper (leave some overhang so you can pull the bread out of the pan). This will keep the loaf from sticking to the pan.

On a lightly floured surface, turn your dough out and roll the dough into a 12×16-inch rectangle. This doesn't need to be perfect!

Spread the softened butter evenly over the dough, leaving a ¼-inch border around the edges. This butter creates a barrier to help the filling avoid leakage.

Add the cooled blueberry compote on top of the butter layer, and spread it evenly over the dough, leaving a ¼-inch border around the edges.

Using a pizza cutter or sharp knife, cut the dough lengthwise into four 3-inch-wide strips.

Next, cut each strip crosswise every 4 inches to create four rectangles per strip. You will have 16 rectangles, each measuring approximately 3×4 inches.

Fold each rectangle in half like a taco with the blueberry filling tucked inside, creating a 3×2-inch folded piece.

Layer each section filling upright into the pan until all the sections are snuggly fitted into the pan.

Cover the pan loosely with plastic and let rise for 45 minutes to an hour, or until the dough is noticeably puffy and the highest layers rise just above the rim of the pan.

This rise is key to a light loaf so don't rush it!

Preheat oven to 350°F (175°C).

Make sure you put a baking sheet on the rack below your loaf to catch any drips or spillage from the filling bubbling.

Transfer the bread to the preheated oven, and bake for roughly 55-60 minutes. Tent loosely with foil during the last 20 minutes to avoid the top over browning.

The bread is done with the bread portion feels firm to touch and the center should register 190–195°F.

Allow the bread to cool while you whip up your lemon cream cheese frosting.

Place the cream cheese and softened butter in a bowl, and beat on high with hand mixers until smooth.

Add the vanilla, powdered sugar, lemon juice, lemon zest and salt to the bowl, and beat into the icing.

Beat milk 1 Tablespoon at at time in to the glaze, until the consistency is runny and can easily drizzle on top of the bread. If the icing is really thick and you need a more thin consistency, you can also warm in the microwave for 15 seconds and beat again for a thinner texture.

Remove the bread from the pan, and drizzle the icing over the top of the warm bread. Zest a fresh lemon on the top for garnish if desired. Serve and enjoy!

Yields 1 loaf