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.