Homemade Twinkie Cupcakes: FILLING: 3 tbsp. unsalted butter, softened; 1/3 c. (42 grams) icing’ sugar; ½ tsp. (5 ml) vanilla; ½ c. marshmallow spread. FROSTING: ½ c. (1 stick or 113 grams) unsalted butter, at room temp; ½ c. marshmallow spread; 1 ½ c. (188 grams) icing’ sugar; 1 to 2 tbsp. (15 to 30 ml) heavy whipping cream; 1 tsp. (5 ml) vanilla extract