Vanilla Peanut Buttercream for whoopie pies

I have never made whoopie pies before but last night I acutally made it. I usually like to buy them at the local grocery store back in New England. I made chocolate chip peanut butter whoopie pies. These were so delicious. I tried out making just 3. I still have the chocolate chip batter and peanut buttercream.

Peanut butter filling

1/3 cup melted butter
1 cup peanut butter

1 1/2 or 2 cups Confectioner sugar

1 1/2 teaspoon vanilla sugar
1 tablespoon regualr milk
1/2 tablespoon vanilla extract

In a bowl mix butter and peanut butter. Gradually mix in the sugar and vanilla sugar. Add in milk and vanilla extract.
Continue mixing until the buttercream is fluffy and easy to spread.