_{In a medium bowl, beat egg yolks until thick and pale. While continuing to beat, gradually sift in flour. Pour into a saucepan and place over low heat on the stove and gradually add milk and vanilla. Cook, stirring constantly, until mixture has thickened to a custard consistency, about 15 minutes. Remove from heat. Melt butter and pour over custard to prevent a skin from forming while it cools.  Makes 3 cups.}