Cut butter into 3 equal portions. Combine 1 portion butter, yolks, and lemon juice in top of a double boiler. Cream together, using a fork, until mixture is smooth.
Place over simmering water, and cook, beating constantly with a wire whisk, until butter begins to melt. Continue to add butter, one portion at a time, beating constantly, until sauce is smooth and thickened. Lift top of double boiler from water occasionally. Remove from heat, and stir in salt and pepper. Serve immediately with baked or broiled fish.