Heat butter and 2 tablespoons of olive oil in a large pot over medium-low heat.

Add chopped garlic and red pepper flakes and cook, stirring, until garlic starts to brown, about 2 minutes.

Add whole peeled tomatoes with their juices and crush them lightly with your hands.

Increase heat to medium-high and cook, stirring occasionally, until the sauce thickens, about 10-15 minutes.

Meanwhile, cook spaghetti in a large pot of boiling salted water until al dente.

Drain the pasta, reserving 1 1/2 cups of pasta cooking liquid.

Add cannellini beans and white wine to the tomato sauce.

Cook, stirring, until the wine has almost evaporated, about 4 minutes.

Add scrubbed and debearded mussels and 1/4 cup of pasta cooking liquid to the sauce.

Cover the pot and cook, stirring occasionally, until the mussels open, about 4 minutes.

Discard any mussels that do not open.

Add the cooked spaghetti and 1/4 cup of pasta cooking liquid to the mussels and stir to coat the pasta with sauce.

Reduce heat to medium and continue stirring, adding more cooking liquid as needed, until the sauce coats the pasta evenly.

Divide the spaghetti and mussels among bowls.

Drizzle with olive oil and garnish with chopped flat-leaf parsley.