1. Prepare the aromatics: Heat the olive oil in a 10-inch oven-safe non-stick skillet over medium heat. Add the chopped yellow onion and cook for 3-5 minutes, until softened and translucent. Stir in the minced garlic and cook for another minute until fragrant, being careful not to burn it. Remove the skillet from the heat for a moment.

2. Whisk the egg mixture: In a medium bowl, whisk together the large eggs, cottage cheese, milk, fresh chives, fresh parsley, fresh dill, salt, and black pepper until well combined. The cottage cheese curds will remain visible, adding a lovely texture.

3. Combine and pour: Pour the egg and herb mixture directly into the skillet with the softened onions and garlic. Gently stir to distribute the onions and garlic evenly throughout the egg mixture.

4. Start on the stovetop: Return the skillet to medium-low heat. Cook on the stovetop for about 8-10 minutes, or until the edges of the flatbread are set and the bottom is lightly golden. The center will still be quite jiggly.

5. Add cheese (optional) and transfer to oven: If using, sprinkle the shredded mozzarella cheese evenly over the top of the partially cooked flatbread.

6. Finish in the oven: Carefully transfer the skillet to a preheated oven at 350 F (175 C). Bake for another 7-10 minutes, or until the center is fully set and the cheese is melted and lightly golden (if used). A knife inserted into the center should come out clean.

7. Rest and serve: Remove the skillet from the oven and let the flatbread rest for 5 minutes before slicing. This allows it to set completely and makes for easier serving.

8. Slice and enjoy: Cut the flatbread into wedges or squares and serve warm.