Chef John's Stuffed Peppers

INGREDIENTS

1 cup

uncooked long grain white rice

2 cups

water

Sauce:

onion, diced

1 tbsp

olive oil

2 cups

marinara sauce

1 cup

beef broth

1 tbsp

balsamic vinegar

1/4 tsp

crushed red pepper flakes

Peppers:

1 lb

lean ground beef

1/4 lb

hot Italian pork sausage, casing removed

1 10 ounce can

diced tomatoes

1/4 cup

chopped fresh Italian parsley

4 cloves

garlic, minced

2 tsp

salt

1 tsp

freshly ground black pepper

1 pinch

ground cayenne pepper

large green bell peppers, halved lengthwise and seeded

1 cup

finely grated Parmigiano-Reggiano cheese, plus more for topping