Fill a large saucepan with water and bring it to a boil over high heat. Add the whole-wheat spaghetti and cook according to the package instructions, stirring occasionally, for about 7 minutes. Turn off the heat and stir in the chopped spinach until it wilts. Reserve ¼ cup of the cooking water before draining the pasta and spinach thoroughly.

A photo of the cooked pasta and spinach mixture

Photographer: Morgan Hunt Glaze, Prop Stylist: Priscilla Montiel, Food Stylist: Julian Hensarling

While the pasta is cooking, heat the olive oil in a large skillet over medium heat. Add the sliced onion and cook, stirring occasionally, until it becomes tender, about 3 minutes. Add the sliced garlic and crushed red pepper, and cook, stirring frequently, until fragrant—this should take about 1 minute.

Pour in the white wine, vegetable broth, salt, and lemon juice. Bring the mixture to a simmer over medium heat and cook, stirring now and then, until it has reduced by about half and slightly thickened, roughly 5 minutes. Add the sour cream and stir continuously until it has fully melted into the sauce, about 30 seconds. Mix in the Parmesan cheese and the reserved pasta water, stirring until the cheese is melted and the sauce is well combined, about another 30 seconds. Add the drained pasta and spinach to the skillet, tossing to coat everything evenly.

A photo of the sauce being prepared with the pasta and spinach added

Photographer: Morgan Hunt Glaze, Prop Stylist: Priscilla Montiel, Food Stylist: Julian Hensarling

Remove the skillet from the heat and stir in the chopped parsley, butter, and lemon zest. Continue stirring until the butter has melted completely, about 30 seconds. Divide the pasta among four serving bowls and garnish with extra parsley and a sprinkle of crushed red pepper, if desired.