Hollandaise is a thick, smooth, pale-yellow sauce. The cook beats egg yolks with butter and adds a little lemon (or a mild vinegar) so it tastes rich and slightly sharp. It is famous on eggs Benedict — poached eggs on a muffin, with ham, and hollandaise on top — and on green vegetables like asparagus. The word is French: hollandaise means Dutch in the feminine form, as in “Dutch sauce.” English borrowed the French name as it was. It is a restaurant and cookbook word, a bit fancy. You do not pour hollandaise on rice at a night market; you meet it in Western food. It is not the same as mayonnaise, though both use egg and can look creamy: hollandaise is warm, made with butter, and usually made fresh; mayonnaise is typically cold and made with oil.