2large or 3 medium fennel bulbs with fronds-cut off tops of fennel, putting aside fronds. Then halve fennel bulbs vertically through root ends, removing tough outer layer and core, thinly slice fennel crosswise
1medium onionhalved and thinly sliced crosswise
½teaspoonkosher saltplus more for seasoning
1teaspoongranulated sugar
4garlic clovesfinely minced or grated or pressed
3oil-packed anchovy fillets
½teaspooncrushed red pepper flakes
12oz.gluten free rigatoni or penne or other medium pasta
1/2cupParmesangrated
2tablespoonsbutterunsalted
1teaspoongrated lemon zest
2tablespoonslemon juicefresh squeezed
Starchy Water
1/2teaspoonkosher salt
1/2teaspooncornstarch
2cupscold water
Instructions
Heat ¼ cup oil in a large Dutch oven or other heavy pot over medium. Add fennel, onion, salt and sugar to the pan and use tongs to stir to combine. Cover and cook, stirring occasionally, until onion is translucent and fennel is beginning to brown around the edges, 8–10 minutes. Uncover and add garlic, anchovies, and red pepper flakes. Stir occasionally, reducing heat as needed to avoid scorching (stir in a splash of water if scorching does occur), until fennel and onion are deep golden brown and very soft and jammy, 12–15 minutes.
Meanwhile, cook pasta in a large pot of boiling salted water, stirring occasionally, until just shy of al dente, about 1 minute less than package directions.
While pasta is cooking, make the starchy water. (This is needed because gf pasta doesn’t have the same starch content as regular pasta which makes it difficult for the sauce to “cling to” the pasta.) To re-create the starchiness found in regular pasta water, try this super simple trick… combine 1/2 teaspoon each of kosher salt and cornstarch with 2 cups cold water in a microwave safe bowl or measuring cup. Heat mixture covered with a paper or cloth towel in a microwave on High for 4 minutes. Set aside.
Drain pasta using a colander and transfer pasta to the pot with the onions and fennel. Add Parmesan, butter, and starchy water to the pot. Increase heat to medium-high and cook, stirring often, until sauce clings to pasta, about 2 minutes.
Then remove pot from heat and stir in most of reserved fennel fronds, lemon zest, and lemon juice. Taste and season with more salt if needed. Transfer pasta to a large bowl and season with more red pepper flakes (if desired) and parmesan and garnish with remaining fennel fronds.