Tiramisu Whoopie Pies

Sorry for the hiatus. This summer has been full of activities and no time for baking (gasp!) and a lack of inspiration (double gasp!). But finally today, my muse is active again and here is what came of that.
Tiramisu Whoopie pies
For the cookies:
1/2 c. Butter
1 1/4c. Granulated sugar
3 eggs
1 tsp. vanilla
1 tsp. baking powder
Preheat oven to 375 degrees F.
In the bowl of your mixer, whip butter until light. Slowly add sugar and continue beating until light and fluffy. Add eggs one at a time and let fully incorporate before adding the next. Add vanilla. Slowly begin adding dry ingredients, scraping down the sides of the bowl occasionally.
Scoop dough onto parchment or silicone mat lined cookie sheets. Bake for 6-8 minutes until the edges just begin to turn golden brown. Transfer to wire rack to cool.
For the filling:
In a small saucepan combine 2Tbs flour, 1/2c. milk and a pinch of salt. Cook until mixture forms a thick paste. Stir constantly or you will have a clumpy mess. Cool completely, in the fridge at least 30 minutes.
In a bowl combine
1/2 c. Butter
1/2 c. Superfine sugar (if you don't have superfine, just toss sugar into a blender, food processor, magic bullet type appliance) This is just so that it doesn't make the frosting gritty.
Beat at high speed, then add the cooled milk/flour paste and add 1 tsp. vanilla and beat until light and fluffy.
Add 8 oz. Mascarpone cheese to the mixing bowl and continue to beat.

To assemble your whoopie pies, lay the cookies bottom side up and generously brush each one with Kaluha or espresso. Then pipe or spoon frosting onto the cookies and sandwich together with another cookie. Dust with some cocoa powder. At this point, if you have some semblance of self control then you can place them in the fridge to firm up just a bit, or if you are like me you will bite into one immediately.