Adjaruli Khachapuri: Georgian Cheese Bread - WILD GREENS & SARDINES

Name: Adjaruli Khachapuri: Georgian Cheese Bread - WILD GREENS & SARDINES
Cuisine: European
Ingredients: Dough; 1 ¾ cup bread flour; 1 teaspoon active dry yeast; ½ teaspoon salt; ½ teaspoon sugar; ½ cup water, room temperature; ¼ cup milk, warmed slightly; 1 ½ teaspoons olive oil; 1 egg for egg wash; Filling; 2 cups sulguni or mozzarella, freshly grated, plus extra for topping each khachapuri; 8 ounces feta, crumbled; 1 whole egg; Splash of brine from feta or milk; 2 egg yolks, plus little bit of the whites; 2 tablespoons butter, room temperature; Red pepper flakes; For the dough