1 pound Brussels sprouts
1 large leek, white and pale-green parts only
4 tablespoons olive oil, divided, plus more for serving
Kosher salt, freshly ground pepper
1 lemon, zest removed with a vegetable peeler, cut into very thin strips
4 garlic cloves, finely chopped
½ cup dry white wine
12 ounces rigatoni
2 ounces Parmesan, finely grated, plus more for serving
Lemon wedges (for serving)
Trim Brussels sprouts with a paring knife, then snap off several dark outer leaves from each; set aside. Cut sprouts into quarters (or halve if very small). Starting at root end, cut half of leek into ½"-thick rings, then chop remaining leek.
Heat 2 Tbsp. oil in a large skillet over medium. Add brussels sprout quarters and leek rings; season with salt and pepper and cook undisturbed until deep golden brown, about 3 minutes. Toss and continue to cook, tossing occasionally, until browned all over and tender, about 3 minutes more. Transfer to a medium bowl.
Set aside a little lemon zest for serving and add remaining zest along with chopped leek, garlic, and 2 Tbsp. oil to same skillet. Season with salt and pepper and cook, stirring often, until garlic and leek are golden, about 4 minutes. Add wine, bring to a boil, and cook until skillet is almost dry, about 3 minutes.
Meanwhile, cook pasta in a large pot of boiling salted water until very al dente, 8–10 minutes; drain, reserving 1 cup pasta cooking liquid.
Add pasta to skillet along with reserved brussels sprout leaves, brussels sprout quarters and leek rings, and ½ cup pasta cooking liquid; toss to combine. Bring to a simmer, then gradually add 2 oz. Parmesan, tossing constantly. Cook, shaking skillet to toss pasta and adding more pasta cooking liquid as needed, until pasta is al dente and sauce is thickened and glossy, about 3 minutes. Season with salt and pepper.
Divide pasta among bowls. Top with more Parmesan and pepper and reserved lemon zest; drizzle with oil. Serve with lemon wedges for squeezing over.