Mocha walnut cake

Ingredients

• 1 cup (220g) caster (superfine) sugar
• 125 grams dark eating (semi-sweet) chocolate, chopped coarsely
• 1 teaspoon instant coffee granules
• 2 tablespoons water
• 125 grams unsalted butter, softened
• 6 eggs, separated
• 2 cups (250g) finely chopped walnuts
• 2 tablespoons plain (all-purpose) flour
• 1/2 cup (60g) coarsely chopped walnuts, extra
• 1/2 cup (125ml) thickened (heavy) cream, whipped mocha frosting
• Mocha frosting
• 60 grams dark eating (semi-sweet) chocolate, chopped coarsely
• 90 grams unsalted butter, softened
• 1 1/4 cup (200g) icing (confectioners') sugar
• 2 teaspoons hot water