Preheat a large, high-sided skillet over medium heat. Add the ground beef and Italian sausage, then cook until browned, breaking the meat apart as it cooks.

Stir in the minced onion, chile flakes, and Italian seasoning. Cook for a few minutes, until the onion begins to soften.

Pour in the white wine and bring the mixture to a boil. Add the tomato puree and stir until everything is well combined.

Reduce the heat to maintain a steady simmer. Cook for 30 to 40 minutes, stirring occasionally, until most of the liquid has evaporated. This step is what keeps the sandwiches neat instead of messy.

Remove the skillet from the heat and divide the meat mixture evenly among the buns. Place the sandwiches on a sheet tray and sprinkle each one with mozzarella. Let some of the cheese fall over the edges of the buns so it browns under the broiler.

Broil until the cheese is melted and lightly browned. Wrap each sandwich in foil or butcher paper to help hold everything together, then serve immediately.