1. Preheat the oven to 350F conventional setting.
2. Line a 12-hole muffin tray with paper cases.
3. Whisk the eggs and sugar in a large mixing bowl for 5 minutes, until pale and quadrupled in size.
4. Add the grated sweet potato and whisk again.
5. Whisk in the ground almonds, flour, peppermint extract, salt, cocoa powder, as well as the baking powder until they are well introduced.
6. Finally, add the chocolate chunks and mix them in with a spatula so that they are evenly dotted around the place.
7. Ladle the mixture evenly between the cupcake cases in the tin. They will come only ½ of the way up the side of the cases, giving them enough space to puff up and rise to the top whilst cooking.
8. Place in a hot oven for 20 minutes until risen and cooked. Don’t be alarmed that they are flat-ish on the top rather than dome shaped. These cupcakes are designed to be tidy and well behaved, rather than rounded and exhuberant. Once cooked, remove from the oven and cool in the refrigerator out of the hot tin (to cool quickly). The cupcakes will need to be cold in order for the icing not to slide off- even a tiny bit of warmth will create havoc so be patient!
9. Store in the refrigerator until the cupcakes are cold through.
10. Once cooked, cool in the tin for 15 minutes. I usually put them into the fridge after this time is up to finish cooling right down so that they are cold by the time you want to ice them.
11. Whilst the cupcakes are cooking, make the icing.
12. Whisk the butter with one heaped tablespoon of the sugar, and the peppermint extract and colouring, for a minute until all incorporated and the butter has softened slightly. Add the icing sugar one heaped tbsp at a time, with ½ tsp of water each time you add the sugar, and beat between each addition.
13. Once all the sugar is added, you should be looking at a soft greenpaste.
14. Ice each cold cupcake, using just over a tbsp of frosting per cupcake.
15. Finish off by sprinkling dark chocolate over the tops of each one.