Nasturtium-Leaf Butter

Bright pistachio-lime green, this deeply nasturtium-flavored butter—its texture lightened with sour cream— holds plenty of pungent leaves. Quick to make, thanks to a food processor’s power, it jazzes up the plainest canapés or sandwiches and fancifies simple poached or broiled fish. Or toss with hot blanched haricots verts, cooked baby carrots, or steamed potatoes.