In a bowl, add starter and water. Dissolve starter. Add oil, flour, egg yolk, salt, and 2 Tablespoons chopped rosemary. Combine well in bowl. Allow to rest covered at room temperature (78 degrees) for 30 minutes.
After 30 minutes, perform a set of stretch and folds. Pick up the dough at the edge of the bowl, and pull up and towards the center. Work your way around the edge to make a ball. Cover and rest again on counter.
Perform two more sets of stretch and folds. After stretch and folds, allow to proof at 78-80 degrees until doubled in size (risen 100 percent).
Shape out 2 loaves. Allow to rise in bannetons covered till doubled ON THE COUNTER. (Here are the mini bannetons I like to use https://amzn.to/3Y1Pvk7) Preheat oven to 450 F. Transfer loaves to parchment paper lined cookie sheet (or silicon mat lined pan, I’ve linked my favorite silicon mats https://amzn.to/4ehDVqA). Brush tops of loaves with 2-3 Tablespoons extra virgin olive oil, and sprinkle with rosemary and flaky sea salt. You can score if you’d like. Place loaves in oven and drop heat to 425 F and bake at 425 F for 20 minutes. Remove from oven and brush with more olive oil. Sprinkle with flaky salt and more rosemary.Makes 2 appetizer loaves