Preheat the oven to 190°C/gas mark 5. Line a 12-hole muffin tin with paper cases.
Put the flour, sugar, cocoa and baking powder into a large mixing bowl and stir to combine.
In a separate bowl, mix together the egg, egg yolk, milk, oil and vanilla extract. Add the wet mixture to the dry ingredients and stir until just combined, without beating. Drop spoonfuls of the caramel into the mixture and gently swirl through, but don’t mix it in completely – you want to still see dollops of caramel in the finished batter.
Spoon the mixture into the paper cases, making sure each case is quite full. Bake in the oven for 20 minutes until springy to the touch. Cool slightly in the tin, and eat warm.