Melt butter over low heat; remove from heat and let sit until the milk solids settle to the bottom; skim the clea butter from the top; discard the sediment. Saute onion and garlic in 2 Tbls. of the clarified butter until transparent. Stir in lemon juice, wine and season with salt and pepper. Simmer 2-3 minutes to reduce liquid. Remove from heat and swirl in cold butter until sauce is smooth and butter is melted.