Chocolate Cream Pie Filling

3 tbsp flour
3 tbsp cocoa
1 cup granulated sugar
1.5 cups milk
3 egg yolks
3 tbsp butter
1 tsp vanilla

Mix flour, cocoa, and sugar.
Slowly add milk, egg yolks and butter (add all of it).
Cook until thick, stirring constantly.
When it is thickened, take the pot off the stove.
Add vanilla and stir it in.
Pour into already baked pie crust.
Refrigerate.