Linguine with Chile, Caramelized Onions, and Gremolata

2 tablespoons olive oil
1 large yellow onion, thinly sliced
? teaspoon crushed red pepper flakes
1 serrano or other small hot chile, finely diced
? cup unsalted butter, cut into 5 pieces
3 tablespoons lemon juice
1 pound dried linguine
1/3 cup gremolata
? cup grated parmesan or pecorino romano

Bring salted water to boil for linguine. Meanwhile, heat oil in 10-inch skillet over medium heat. Add onion and red pepper flakes, season with salt, and cook until tender and nicely browned, about 15 minutes. Add chile and cook 1 minute more. Remove from heat and add butter, swirling pan to melt. Add lemon juice and pinch of salt. Keep warm.

Cook linguine, drain, and return to cooking pot. Over medium heat, add onion mixture and toss to combine. Add cheese and toss again. Place in serving bowls and top with gremolata.

from Fine Cooking.