In a mixing bowl sift the dry ingredients and mix. Set aside.
In an electric mixer, combine the butter and sugar and whisk until pale.
Add the eggs one at a time to incorporate.
Add the vanilla essence and lime – whisk until just incorporated.
Now combine the dry and wet ingredients by adding a little of the dry ingredients to the wet ingredients and alternating between adding the milk as well.
Mix until incorporated and set aside. Fill the prepared muffin tins 3/4 full with batter and bake for 15 – 20 min at 180 degree Celsius.
Leave to cool, then combine the mascarpone cheese with lime juice and mix well.
Assemble the whoopie pies by cutting each cupcake in half, and filling it with mascarpone, topping it with the top part.
Dust with icing sugar and more lime zest. Ready to serve.