Spelt Flour Chocolate Fudge Cake (Adaptable)

Name: Spelt Flour Chocolate Fudge Cake (Adaptable)
Cuisine: American
Ingredients: butter (for greasing); 240g (2 cups) spelt flour (see note 1); 320g (1½ cups) granulated sugar; 80g (¾ cup) cocoa powder; ½ tablespoon baking soda; ¾ teaspoon baking powder; ½ teaspoon salt; 2 large eggs; 100ml (3½ oz) Greek yoghurt (see note 2); 80ml (¼ cup + 1 tbsp) milk (see note 2); 60ml (¼ cup) vegetable oil; 2 teaspoons vanilla extract; 200ml (⅚ cup) hot water; 1 tablespoon instant coffee (see note 3); 100g (4 oz) dark chocolate; 75g (⅓ cup) butter (chopped into small pieces); 118ml (½ cup) milk; 550g (4½ cups) icing sugar; Chocolate shavings and gold decorations (optional)