Stuffed Shells

Oooh baby. This is one of my favorite dishes, ever. 
4 oz. Pancetta (thinly sliced from deli)
1/2 med. white onion (diced)
2 28 oz can of Crushed Tomatoes
1 lg garlic clove
pinch of pepper flakes
2 T Olive Oil

Add the crushed tomatoes
Meanwhile, boil shells

Cheese mixture: 
1 Egg, beaten
16 oz Ricotta
1/2 C grated Parmesan
small handful of shredded Mozzerella
handful of fresh parsley, chopped
pinch of Kosher salt & a few twists of fresh cracked pepper
Stuff this little babies
Season sauce w/ salt before topping
Top 'Em w/ sauce & cheese & place in 350º oven