Fill a large pot with water, cover it, and bring it to a boil over high heat.

While the water heats, drain and rinse the cannellini beans in a colander. Finely chop the shallot and parsley, slice the garlic, and measure the pepperoncini and 2 tablespoons of its brine.

When the water comes to a full boil, add 1 tablespoon kosher salt.

Put the spaghetti into the boiling water and stir for the first 30 seconds so the strands do not stick together.

Set a large skillet on the stove over medium heat and add the olive oil.

Add the chopped shallot to the skillet. Cook for 2 to 3 minutes, stirring often, until it softens and looks lightly translucent.

Add the sliced garlic to the skillet. Cook for about 30 seconds, stirring, just until it smells fragrant and does not brown.

Scoop 3/4 cup of the hot pasta water into a measuring cup and set it near the stove.

Put half of the beans, the pepperoncini brine, and 1/2 cup of the hot pasta water into a blender or a tall cup for an immersion blender. Blend until the mixture is very smooth.

Add the remaining whole beans and all of the sliced pepperoncini to the skillet. Stir for about 1 minute, just to warm them through.

Pour the blended bean mixture into the skillet. Let it bubble gently for 2 to 3 minutes, stirring once or twice, until it thickens slightly.

Taste a strand of spaghetti. When it is tender with a little firmness in the center, use tongs to transfer the spaghetti from the pot directly into the skillet.