In a large mixing bowl, whisk warm water (about 105–110°F / 40–43°C) with the sugar and instant yeast. Let sit 5 minutes until foamy. Stir in warm milk, melted butter, and the whole egg until combined.

Mix dough

Add the flour and salt to the liquid mixture. Stir with a wooden spoon or a dough hook on low speed until a shaggy dough forms.

Knead

Knead by hand on a lightly floured surface or with a stand mixer fitted with a dough hook for 6–8 minutes until the dough is smooth, elastic, and slightly tacky. If dough is too sticky, add up to 2 tablespoons more flour; if too dry, add 1–2 tsp water.

First rise

Shape dough into a ball, oil a large bowl lightly, place dough in bowl turning once to coat with oil. Cover with plastic wrap or a clean towel and let rise in a warm draft-free place until doubled in size, about 60–75 minutes.

Filling

Cook sausage and aromatics

While the dough rises, heat 1 tablespoon olive oil in a skillet over medium heat. Add the removed sausage meat, breaking it up with a spatula. Cook until no longer pink and beginning to brown, about 6–8 minutes. Push sausage to the side and add diced onion and red bell pepper; cook 4–5 minutes until softened. Add minced garlic and cook 30–45 seconds until fragrant. Drain any excess fat from the pan.

Combine filling

Transfer the cooked sausage mixture to a bowl to cool slightly. Stir in ricotta, shredded mozzarella, grated Parmesan, chopped parsley, dried oregano, crushed red pepper flakes, 1/2 tsp salt, and 1/4 tsp black pepper. Taste and adjust seasoning. The mixture should be moist but not overly wet—if very wet, let it cool and drain a bit.

Assembly & Finish

Roll out dough

After the dough has doubled, punch it down and turn it onto a lightly floured surface. Roll or press into a rectangle about 12 x 16 inches and roughly 1/4 inch thick.

Spread filling

Evenly spread the cooled sausage-cheese filling over the dough, leaving a 1/2-inch border along one long edge. Press filling gently so it adheres but does not cause the dough to tear.

Form the loaf

Starting from the long edge opposite the border, tightly roll the dough into a log. Pinch the seam closed and tuck the ends under to seal. Place the loaf seam-side down on a parchment-lined baking sheet or into a greased 9 x 5-inch loaf pan for a traditional loaf shape.

Second rise

Cover loosely with plastic wrap or a kitchen towel and let rise again in a warm place until puffy, about 30–40 minutes. Preheat oven to 375°F (190°C) during the last 15 minutes of this rise.

Egg wash and seeds

Whisk the egg with 1 teaspoon water. Brush the top of the risen loaf with the egg wash and sprinkle sesame seeds evenly if using.

Bake

Bake on the middle rack for 30–35 minutes until the crust is golden brown and internal temperature of the bread reaches about 190–200°F (88–93°C). If the top browns too quickly, tent loosely with foil for the last 10 minutes.

Cool and serve

Remove from oven and let cool on a wire rack for at least 15 minutes before slicing. Cool further for cleaner slices if time allows. Serve warm or at room temperature.