• Preheat the oven to 350F/175C degrees. Grease a 12 section mini cake pan or mini loaf pan. Note: if using a mini loaf pan, you may not get 12 cakes out of the recipe.
• Into a large bowl, sift together the flour, sugar, baking powder, and salt.
• In a small bowl, whisk together the egg, melted butter, zest and juice.
• Add the food coloring if using. Mix until well combined.
• Stir the milk into the dry ingredients followed by the juice mixture and stir until just combined. 
• Spoon the batter into the baking pans, filling each one a little more than three-quarters full.
• Bake for 15-17 minutes, until a cake tester comes out clean.
• Allow to cool for 5 minutes, then tap the cakes out and transfer to a rack to completely cool.
• Place baking paper under wire racks to catch the excess icing.

For the icing:

• Prepare by mixing the sugar, butter and zest together in a bowl and then add the juice one tablespoon at a time until the desired consistency is reached (I like mine fairly thick).
• Dip the cooled cakes into the icing one at a time covering half the doughnuts then place on the cooling wracks.
• Add the candies before the icing sets (if using)
• Leave on cooling rack to completely set the icing before serving.