Baked Ziti with Sausage and Ricotta

1 yellow onion, finely chopped

3 garlic, minced

10 g basil, roughly torn

340 g italian sausage, casings removed

450 g ricotta, whole milk

1 egg, lightly beaten

60 g parmesan cheese, grated

340 g mozzarella, shredded

450 g ziti pasta

15 ml olive oil

800 g crushed tomatoes

60 g tomato paste

10 ml dried oregano

2 ml red pepper flakes

10 ml kosher salt, divided

5 ml black pepper, freshly ground