Cut the cake circles. Using a 2-inch round cookie cutter, cut 2 circles out of each pound cake slice (8 circles total).
Make the buttercream. Add butter, sifted powdered sugar, heavy cream, and vanilla extract to a bowl. Whip with a hand mixer until smooth and fluffy.
Fill the piping bags. Spoon buttercream into one zip-top bag and raspberry jam into another. Seal, then snip a tiny corner off each bag.
Assemble each mini cake. Pipe buttercream onto one cake circle, then pipe jam on top. Add a second circle. Pipe a final layer of buttercream on top.
Garnish. Top each mini cake with a fresh raspberry and mint leaf just before serving.
Repeat for all 4 mini cakes.