Add the warm water (roughly 120°F or less) to your large mixing bowl (or the bowl of a stand mixer). Mix in the active dry yeast and sugar. Let rest about 5 minutes while the yeast blooms.

Add the warm milk, sourdough discard, softened butter, and the egg plus egg yolk (preferably room temperature). Mix until combined.

Add the flour and salt. Mix by hand or in a stand mixer on low speed until a smooth ball forms.

Knead 5–10 minutes, or until the dough passes the windowpane test (you can stretch it thin enough to see light through without it breaking). Don't worry about over-kneading.

Let rest in a greased bowl about an hour, or until doubled in size.

While the dough rises, make the garlic-herb butter: in a bowl, mix the softened butter, mozzarella, parmesan, salt, garlic powder, dried parsley, and dried thyme. Set aside.

Once proofed, place the dough on a lightly floured surface and divide into 12 equal balls (about 70g each).

Flatten each ball (they don't need to be uniform) and place about 1 tablespoon of filling on each. Lightly spread to cover all the dough — if you have leftover filling, melt it and brush over the loaf before baking.

Fold each piece over the filling like a taco and lightly stretch into a rectangle about as wide as your loaf pan.

Place the 12 pieces upright in a buttered loaf pan, one after the other. Cover and let rise in a warm spot for 30–45 minutes, until noticeably puffy. Toward the end of the rise, preheat the oven to 375°F.

Bake 40–45 minutes, until golden brown and baked through (an internal temperature of at least 180°F). If the top is browning too quickly, tent loosely with foil for the last 10–15 minutes.

Top with melted butter and enjoy warm!