Ingredients
Method
Cut stalks from 3 large fennel bulbs with fronds and cut fronds from stalks; discard stalks. Coarsely chop fronds and set aside. Remove tough out layer from bulbs and discard. Halve bulbs lengthwise (through root ends) and remove cores; discard. Thinly slice bulbs crosswise.
Heat ¼ cup extra-virgin olive oil in a large Dutch oven or other heavy pot over medium. Add fennel bulbs, 1 medium onion, thinly sliced, 1 tsp. Diamond Crystal or ½ tsp. Morton kosher salt, and 1 tsp. sugar; 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 4 garlic cloves, finely chopped, 3 oil-packed anchovy filets, and ½ tsp. crushed red pepper flakes. Cook, stirring occasionally and 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, 15–20 minutes.
Meanwhile, cook 12 oz. gemelli, fusilli, or other medium pasta in a large pot of boiling salted water, stirring occasionally, until just shy of al dente, about 1 minute less than package directions.
Using a slotted spoon, transfer pasta to pot with sauce. Add 1 oz. Parmesan, finely grated (about ½ cup), 2 Tbsp. unsalted butter, and 2 cups pasta cooking liquid. Increase heat to medium-high and cook, stirring often, until sauce clings to pasta, about 2 minutes. Remove from heat and stir in 1 cup reserved fennel fronds, 1 tsp. finely grated lemon zest, and 2 Tbsp. fresh lemon juice. Taste and season with more salt if needed.
Divide pasta among shallow bowls and top with more reserved fennel fronds.