Cook the Pasta: Bring a large pot of salted water to a boil over high heat. Add your favorite pasta and cook according to package instructions, usually 8-10 minutes until al dente. Reserve 1 cup of the pasta water and drain the pasta.

Sauté Onion and Garlic: In a large skillet, heat olive oil. Add the diced onion and minced garlic, seasoning with salt, black pepper, and optional red pepper flakes. Sauté for about 5-7 minutes until onions become translucent.

Blend the Sauce: Transfer sautéed mixture to a blender with white beans and lemon juice. Add ½ cup of reserved pasta water and blend until smooth.

Combine Sauce and Pasta: Return the blended sauce to skillet over low heat. Adjust thickness with additional pasta water and taste to season.

Toss Pasta in Sauce: Add drained pasta to the skillet, tossing to coat it in the sauce. Heat for 1-2 minutes.

Serve and Garnish: Dish the pasta into bowls and garnish with fresh parsley. Serve hot.