Throw a lemon—rind, pith, seeds, the whole shebang—into a blender with olive oil, blitz the heck out of it, and what do you get? A bright and bracing emulsion that's terrific in everything: tossed with roasted potatoes, added to marinades, even mixed into pancake batter for some zip. Refrigerated, it can keep for three weeks, but it doesn't last nearly that long in my house.