In a large bowl, whisk together the semolina flour, all-purpose flour, yeast, and salt.

Add the warm water and olive oil. Mix until a shaggy dough forms, then turn it out onto a lightly floured counter.

Knead for 8 to 10 minutes until the dough is smooth and springs back when poked. Shape into a ball, place in an oiled bowl, cover, and let rise for 60 minutes, until roughly doubled.

While the dough rises, heat 2 tbsp olive oil in a 26 cm / 10-inch skillet over medium heat. Add the diced onion and cook for 4 to 5 minutes until soft.

Add the crumbled sausage and cook for 6 to 8 minutes, breaking it up with a spoon, until no pink remains.

Stir in the crushed tomatoes, oregano, salt, and pepper. Simmer for 15 minutes, stirring occasionally, until the sauce thickens and coats the back of a spoon. Remove from heat and let cool completely, at least 20 minutes; warm filling makes the crust soggy.

Heat the oven to 190C / 375F. Punch down the risen dough and divide it into two pieces, one slightly larger than the other.

Roll the larger piece on a floured surface into a 30 cm / 12-inch circle and line a 23 cm / 9-inch springform pan or deep pie dish, letting the edges hang over the rim.

Spread half the cooled sauce over the base, scatter half the caciocavallo and olives, then repeat with the remaining sauce, cheese, and olives.

Roll the second piece of dough into a 25 cm / 10-inch circle and lay it over the filling. Fold the overhanging edge up and over, crimping to seal. Cut 2 to 3 small steam vents in the top.

Brush the top with beaten egg. Bake for 35 to 40 minutes, until the crust is deep golden brown and the filling bubbles through the vents.

Cool in the pan for 15 minutes before slicing, so the filling has time to set.