Pasta with Guanciale, Tomato, and Chile

This recipe comes from Tosca in San Francisco and was published in Bon Appetit. It's very good. I upped the amounts so I could cook a full pound of pasta which really just amounted to adding more rosemary and 5 ounces of crushed tomatoes. I've made this with and without garlic and personally I like it a little better with some garlic (just 1 large clove). 

1 sprig rosemary
4 ounces guanciale (salt-cured pork jowl) or pancetta, very thinly sliced
½ medium red onion, finely chopped
1 15-oz. can crushed tomatoes
1 teaspoon crushed red pepper flakes
12 ounces bucatini
Kosher salt
1 ounce Pecorino, finely grated
Olive oil (for serving)

Microwave rosemary on high in 20-second intervals until leaves are brittle, about 60 seconds. Remove leaves and grind to a fine powder with a spice mill or mortar and pestle; you should have about 1 tsp. (Alternatively, very finely chop leaves.)

Cook guanciale in a large skillet over medium heat, stirring often, until guanciale is browned and crisp, 10–12 minutes. Transfer to a bowl with a slotted spoon.

Cook onion in same skillet over medium heat, stirring often, until softened and golden brown, 8–10 minutes. Return all but 2 Tbsp. guanciale to skillet and add tomatoes, red pepper flakes, and rosemary powder. Bring to a boil, reduce heat, and simmer, stirring occasionally, until sauce is thickened, 5–8 minutes.

Meanwhile, cook pasta in a large pot of boiling salted water, stirring occasionally, until al dente, 8–10 minutes. Drain pasta, reserving 1 cup pasta cooking liquid.

Add pasta and ½ cup pasta cooking liquid to sauce. Cook over medium heat, tossing and adding more cooking liquid as needed, until sauce coats pasta, about 2 minutes.

Serve pasta topped with Pecorino and remaining 2 Tbsp. guanciale and drizzled with oil.