Preheat the oven to 180C/350F/gas mark 4
Use a 20cm/8 inch square cake tin.
Grease and flour the cake tin. Cream the butter and sugar together until light and fluffy. Add vanilla essence, sour cream and milk and mix until well combined. Fold in the flour and ground hazelnuts. Pour into the prepared tin and bake for 45 to 50 minutes or until a warm knife inserted in the middle comes out clean. Cool completely in the tin before removing. Icing. Beat the ingredients together until smooth. Spread over the cake and sprinkle with chopped hazelnuts.
