Cream butter and sugar together with an electric mixer until light and fluffy, about 3 minutes. Add melted chocolate and espresso powder to the butter and sugar mixture. Whip in vanilla and sour cream until light and fluffy. Pour into pre-baked pie crust and chill for at least one hour before serving. Serve with optional whipped cream.
If eggs are not of concern for you, you can use two lightly beaten eggs instead of sour cream for a classic French Silk Pie recipe.
French Silk Pie Recipe https://addapinch.com/french-silk-pie-recipe/