Cook your pasta of choice in salted water according to the package directions. (Reserve 1 cup of the cooking water.)
While your pasta is cooking, peel and dice an onion and mince 3 cloves of garlic. Then sauté them over low heat in 3 tablespoons of olive oil with a sprinkle of salt, pepper, and red pepper flakes until the onions are translucent.
Add the sautéed onion and garlic, along with a teaspoon of lemon juice, to the blender. Then add a can of drained white beans to the blender along with 1/2 cup of the reserved starchy pasta water.
Blend the mixture until very smooth. Add the remaining 1/2 cup of the reserved pasta water and blend again until the mixture is very smooth.
Pour the white bean cream sauce back into the frying pan used to sauté the onions and warm it over low heat. Add salt and pepper to taste if needed.
Toss in the cooked, drained pasta and stir to coat it with the sauce. Garnish with fresh parsley and serve hot.
Notes
Add a tablespoon of nutritional yeast or a teaspoon of soy sauce (or Tamari) for extra umami flavor.
Sauté the onion and garlic over low heat to bring out the onion's sweetness and avoid burning them.
The sauce will thicken slightly as it cools, so you want it to be fairly thin when it's hot.