Preheat your oven to 325 degrees. Spray your whoopie pan lightly with cooking spray.
Place all of your ingredients in a large bowl. Stir with a spoon to combine. Using an electric mixer, mix at medium speed for about 2 minutes being sure to scrape the bowl a few times.
Spoon ~2 tsp of mix into the whoopie pie pan. Spread around the cup of the pan. Each cup should be about 1/3 full.
Bake in 325 degree oven for 8-10 minutes. Cool completely.
While the pies are cooling, beat the butter with the mixer until smooth. Add sugar, 1/2 cup at a time, with the mixer running. Once the sugar is incorporated, beat in the Riesling.
Frost 1 whoopie pie cake and top with a second piece of "cake."