Grease and line a cupcake tin with butter and preheat the oven to 180C/160C Fan/ Gas Mark 4.
Cream the softened butter in mixer at medium speed until pale and creamy then add the maple syrup gradually. Using a spatula every now and then scrape the mixture from the sides into the middle. Continue mixing until the butter and maple syrup combine to give a creamy mixture.
Weigh out the flour into another bowl and add a pinch of salt.
Add the egg yolks one at a time to the maple butter mixture and combine well, alternating with sieved flour.
Dissolve the coffee granules in the hot water and add this slowly to the above mixture.
Whisk the egg whites to form stiff peaks and fold this into the cake mixture.
Spoon the cake mixture into the cupcake tin about 2/3 full.
Bake for 20 minutes.
While cakes are in the oven start the buttercream by whipping up the butter then gradually add the icing sugar, sieving it with each addition. Then add 1 tbsp of maple syrup and milk.
When the cakes are baked place them on a wire rack and leave them for 5 minutes before removing them from the tin. Allow them to cool completely before icing.
Cut the cakes in half, fit a star nozzle on the end of a piping bag. Sandwich the 2 halves together and then decorate the top of each cake with swirls.