This is another great recipe from the folks at Cook’s Illustrated. I refer to their books and website more than any others whenever I’m cooking something for the first time because I know I’ll always get great results from their recipes. I subbed out olive oil with more butter and increased the amount of garlic.
Heat butter in a large skillet over medium-high heat. When the butter melts and the foam subsides, add the pepper flakes, garlic, and anchovies and cook, breaking up the anchovy fillets, with a wooden spoon, until the mixture is fragrant (~1 minute).
Add the mushrooms and cook, stirring occasionally, until the liquid from the mushrooms has evaporated and the mushrooms are lightly browned, about 12 minutes. Season with salt to taste, squeeze on the juice from one lemon (if using), and serve immediately.