Melt butter over low heat in a 1-quart saucepan. The fat will rise to the top, and the milk solids will sink to the bottom. Remove from heat. Skim the white froth off the top. Strain off the clear yellow butter, keeping back the sediment of milk solids. Discard the milk solids. Combine the clarified butter, mustard, and lemon juice, mixing well.
Oxmoor House Homestyle Recipes