|1 small yellow onion (peeled and roughly chopped)|
|2 cloves garlic (peeled)|
|1 tbsp extra virgin olive oil|
|1/8 tsp red pepper flakes|
|6 oz orecchiette pasta (reserve 1 cup of pasta cooking water)|
|1/4 cup tomato paste|
|1 (14-ounce) can cannellini white beans (drained and rinsed)|
|1 tbsp salted butter|
|1/2 cup rosemary arugula pesto|
Set a large pot of water on the stove and bring to a boil
Meanwhile, place the onion and garlic in the bowl of a food processor and pulse until pureed.
Heat the olive oil in a large pan set over medium heat.
Add the onion-garlic puree along with the red pepper flakes.
Cook, stirring frequently, until the onions have softened and lost their bite; about 8 to 10 minutes.
Meanwhile, add the pasta to the boiling water and cook 1 or 2 minutes shy of al dente according to package directions (until there is just the slightest bite left in the center).
When the pasta is nearly done cooking, add the tomato paste and beans to the onion-garlic mixture.
Strain the pasta, reserving 1 cup of cooking water.
Add 1/2 cup of the reserved cooking water to the tomato-onion mixture and cook for 2 to 3 minutes, until well-combined and slightly reduced.
Add the butter and drained almost-al dente pasta to the pan and toss well.
Add enough of the remaining half cup pasta cooking water to mostly submerge the pasta. Cook until the pasta is tender and the sauce is very thick, another 2 to 3 minutes.
Stir half of the pesto into the pasta; taste and add salt as desired.
Serve hot, with crusty bread and fresh arugula (optional). Garnish with the remaining pesto.