Roman-Style Meatballs with Gnocchi alla Romana

1 1/2 cups fresh bread crumbs 

1/2 cup milk 

4 oz. finely chopped prosciutto 

1 lb. ground beef 

1 lb. ground pork 

2 eggs, lightly beaten 

1/2 cup grated Parmigiano-Reggiano cheese 

2 Tbs. finely chopped fresh flat-leaf parsley 

2 tsp. finely chopped fresh oregano 

6 Tbs. finely chopped fresh basil 

5 garlic cloves, minced 

1 tsp. kosher salt, plus more, to taste  

1/2 tsp. freshly ground pepper, plus more, to taste 

5 Tbs. olive oil 

1 yellow onion, diced 

1 can (28 oz.) crushed tomatoes with juices 

Gnocchi alla Romana for serving