Preheat your oven to 160 degrees and line the base and sides of a 20cm round cake tin.
Place the softened butter and caster sugar into the bowl of an electric mixer and combine until light and fluffy.
Add the eggs one at a time and mix well in between.
Place the coffee, vanilla extract in a small bowl and add 1 tablespoon of warm water. Mix until the coffee has dissolved. Add this coffee mixture and beat well to combine.
Remove the bowl from the mixer stand and using a large metal spoon fold through the sifted flours and sour cream.
Spoon the mixture into your prepared cake tin and gently smooth the surface before placing into the over to bake for 45 minutes or until cooked through when tested with a skewer.
Let the cake cool in the tin for 5 minutes before carefully transferring to a wire rack to cool completely.
Once the cake has cooled, prepare the icing by dissolving the coffee in 1 - 2 tablespoons of warm water before adding to a small bowl with the icing sugar and butter. Mix well until combined and spread over the cooled cake.