Step 1

1 In a deep, wide, lidded skillet over medium-high heat, heat the olive oil until it shimmers

Step 2

2 Add the onion, mushrooms, 1/2 teaspoon of salt and the thyme and cook, stirring occasionally, until the onion and mushrooms begin to caramelize, about 10 minutes

Step 3

3 Stir in the garlic and cook for 1 more minute

Step 4

4 Stir in the white wine, if using

Step 5

5 Transfer the onion and mushroom mixture to a bowl

Step 6

6 To the same skillet, add the spaghetti, enough water to cover by 1 inch, and the remaining 1 teaspoon of salt

Step 7

7 Cover and bring to a rolling boil

Step 8

8 (This shouldn’t take long as the skillet will still be quite hot

Step 9

9 ) Cook until al dente, about 10 minutes

Step 10

10 Reserve 1 cup of the pasta water; drain the pasta, leaving some water clinging to it, and return it to the skillet

Step 11

11 Keep warm over very low heat

Step 12

12 In the pitcher of a blender, combine 1/2 cup of reserved pasta water, the beans and their liquid

Step 13

13 Parmesan and pepper and blend until very smooth

Step 14

14 Pour the mixture over the pasta

Step 15

15 Add the cooked onion and mushroom mixture, chicken, if using, and sour cream, if using

Step 16

16 Stir until the pasta is well-coated in the sauce

Step 17

17 If it seems a little dry, add more pasta water

Step 18

18 The pasta can be served family-style, right from the skillet or, if desired, baked in a casserole dish

Step 19

19 If baking: Position a rack in the middle of the oven and preheat to 350 degrees

Step 20

20 Grease a 9-inch square baking dish with olive oil

Step 21

21 Transfer the pasta mixture to the greased dish, and sprinkle with additional Parmesan, if desired

Step 22

22 Bake for about 15 minutes, or until the cheese is mostly melted and the pasta is very hot but not dry

Step 23

23 Serve family-style

Step 24

24 NOTE: To make this recipe vegan, omit the chicken and cheese, and add 1/4 cup of nutritional yeast and 1 teaspoon of dry mustard to the sauce