Place the pistachio nuts in a food processor and pulse until you reach a fine powder. Don’t worry if there are still a few lumpy bits and be careful not to pulse until the pistachios turn into nut butter. Set aside.

Using a stand/hand mixer, beat the eggs and sugar together until light and fluffy (about 2-3 minutes). With the mixer still on, gradually add the melted butter and mix until just combined. Sift the plain flour and baking powder into the bowl and using a spoon, fold to combine. Add the pistachio flour and continue to fold until well incorporated.

Pour the mixture into the prepared cake pan and bake for 20-25 minutes or until the cake has come away from the sides of the cake tin and a cake skewer comes out clean.

Leave to cool in cake tin for 5 minutes before inverting onto a cooling rack. Once completely cool, dust with icing sugar.