Coffee and Walnut Cake

Sponge

• 175 g unsalted butter, diced, plus extra for greasing
  ή 175 g margarine, plus extra for greasing
• 175 g golden caster sugar
• 3 large eggs
• 175 g self-raising flour
• 1 tsp baking powder
• 3 Tbsp instant coffee, dissolved in 2 Tbsp boiling water
• 60 g walnuts, chopped

Icing

• 200 g icing sugar
• 100 g unsalted butter, soft
• 1 Tbsp instant coffee, dissolved in 1 Tbsp boiling water
• 8 halved walnuts