Switch to a spatula and add in the dry ingredients alternating with buttermilk in three passes. Start and finish with dry ingredients. Do not overmix.
½ cup Buttermilk
Fill the liners up to ⅔ and bake for 10-13 minutes. Let them cool down completely.
How To Make The Frosting
Use the paddle attachment, and beat the butter and cream cheese until smooth and lump-free.
1 cup Butter, ½ cup Cream cheese
Add the meringue powder to one cup of the powdered sugar and mix well. Add this powder to the butter mixture in spoonfuls and mix well. Add the remaining of the sugar.
3 Cups Powdered sugar, 1 teaspoon Meringue Powder
Add in vanilla extract, champagne, and heavy cream. Beat the mixture for 2-3 minutes until the mixture is light and fluffy. If the mixture is too soft, add more powdered sugar, one tablespoon at a time. And if it is too stiff add more cream.