Prepare basic cream puff recipe as above. Let cool.
Heat milk in large heavy saucepan until bubbles appear around edge. Beat egg yolks and sugar in a large bowl with wire whisk or mixer until pale yellow and thick. Beat in flour until well mixed. Gradually beat in hot milk; pour all back into saucepan. Cook, stirring constantly, over moderately high heat until mixture thickens and comes to boiling, lower heat. Mixture will be lumpy in the beginning, but lumps disappear during cooking and stirring. Continue cooking 2 to 3 minutes, over low heat, stirring constantly. Mixture will be quite thick.
Remove from heat. Stir in butter and vanilla. Place a piece of wax paper directly on surface of filling to prevent skin from forming.
Chill at least 2 hours. If filling becomes too stiff after it's chilled, gradually stir in 2 to 4 tablespoons cream or milk, 1 tablespoon at a time.
To make chocolate filling following the directions for Vanilla Custard Filling, adding 1tbs + 1tsp chocolate coco powder stirring until combine. Continue with rest of recipe. Fill puffs just before serving.