For the espresso cardamom buttercream:

1. Warm the milk on the stove or in the microwave until steaming but not boiling.
2. Mix in the espresso powder until dissolved. Set aside to cool.
3. Place the butter in the bowl of a stand mixer and beat until butter is pale in color and creamy. Mix in the cardamom and powdered sugar. With the mixer running on medium, add the milk espresso mixture slowly. Increase mixer speed and beat until light and fluffy, about 3-5 minutes.

For the naked cake design:

1. Place a cake layer on your platter or turntable with the domed side up. Use the cake leveler or a serrated knife to level off the domed part of the cake.
2. Place a large dollop of buttercream frosting on the leveled layer and use an offset spatula to spread evenly, about 3/4 inch thick. Put in the fridge to chill 5 minutes.
3. Level the next cake layer and place it on top of the buttercream. Cover with buttercream. Repeat with the remaining layers, with the top layer having the cut side down.
4. Cover the entire cake with a layer of buttercream, using the bench scraper to remove all but a thin layer. For a great video on frosting, a naked layer cake, check out this one (just stop when she puts the whole cake in the fridge).