1. For the frosting: To make the frosting, beat softened butter and Double Crème White until smooth.
2. Add the pesto and chili sauce and stir until combined. Let it set in the fridge.
3. For the filling: Chop the onions and leeks.
4. Cook the onions slowly in butter in a frying pan over medium heat.
5. When they start to brown add the sugar to kick start the caramelization process. The onions are done when they have turned completely golden brown.
6. Remove the onions from the pan and saute the leeks briefly. Let both cool
7. For the cupcakes: Preheat the oven to 350°F (fan)
8. Whip the butter until light and airy. Add sugar and whip until fluffy. Beat in the eggs one at a time.
9. In another bowl, combine flour, baking powder, cayenne pepper and thyme. Combine the dry and wet ingredients and then carefully add the grated Extra Mature Cheddar.
10. Fill each baking cup with about 1 tablespoon batter to cover the bottom. Place some onions and leeks in the middle then top with more batter.
12. Bake for about 25-30 min. until golden and crisp. Let them cool before decorating with the cheese frosting and a little fresh thyme.