How to make Brazo de Mercedes

• Beat the egg whites with the cream of tartar until stiff.
• Add the sugar gradually and beat until smooth.
• Line a jelly roll baking pan with wax paper and grease.
• Pour the egg white mixture onto the pan.
• Bake at 350 °F oven until brown.
• Remove from the oven and invert on a greased wax paper.
• Peel off the lower wax paper lining. Set aside and cool.
• Make the filling by combining the egg yolks with milk.
• Place on the top of a double boiler and whisk until thick and smooth, stirring constantly. Continue whisking and add 1 tablespoon of butter at a time.
• Spread on baked egg white. Roll and chill. Good for 4 to 6 persons.