In a saucepan, simmer milk over low heat until reduced to 2 cups. Add sugar, butter, and vanilla extract, stirring constantly. Remove from heat.
Beat egg yolks in mixing bowl. Add a little of the milk to the egg yolks, stir, then gradually add mixture by spoonfuls back into the saucepan, beating constantly. Stir well to avoid curdling.
Add cashew nuts and continue cooking entire mixture over low heat, stirring constantly, until mixture has the consistency of a paste. Set aside.
Preheat oven to 400 degrees. Combine eggs and Cream if Tartar then Beat egg whites until stiff. Gradually add 1 cup sugar, beating continuously. Stir in vanilla.
Line a large cookie sheet with parchment paper greased with butter and spread meringue on top. Bake until brown.
Spread filling evenly on top of meringue and roll into a log.
Brush with butter and brown again in oven.