Step 1 of 4

Sweat the leeks under a lid, no color

Melt the butter in a large pot over low heat, add the leeks and a teaspoon of the salt, cover, and cook for 12 minutes, stirring twice. They should end up limp and pale, not browned at all.

— The lid traps the leeks' own steam so they soften without frying. If you hear sizzling rather than a quiet bubble, the heat is too high.