First prepare the vanilla filling as it needs to be well-chilled. In
a saucepan, bring the milk to a boil over medium heat. Mix the egg
yolks, egg, sugar, starch and vanilla until smooth. Remove the boiling
milk from heat and mix in the egg mixture, stirring constantly. Return
to the heat and cook until it boils again; allow it to boil boiling for
at least two minutes. Stir con- stantly with a whisk. Remove from heat
and stir in the butter. Cover the filling with a plastic wrap in direct
contact and allow to cool completely.
Afterwards, prepare the sponge cake batter. In a smaller bowl,
combine all the dry ingredients with a whisk. In another, larger bowl,
mix the egg, milk and coconut oil using a hand mixer. Add the dry
ingredients to the wet ingredients and mix with a hand mixer until just
Preheat the oven to 160 °C (325 °F). Line the muffin tin with paper
liners. Reserve about 450 g vanilla filling and refrigerate, fill the
piping bag with a round nozzle with the rest of the filling. Fill each
paper liner with one teaspoon of the batter, pipe on some vanilla
filling and cover with another teaspoon of the batter, spreading it with
a teaspoon (any filling peeking out of the batter will spread during
baking). The batter makes 12 lovely flat cupcakes suitable for frosting.
Place the tin in a preheated oven and bake for 20 minutes. Take the
baked cupcakes out of the oven and leave them in the tin to cool for 5
minutes. Cool the cupcakes completely on a cooling rack.
Mix the mascarpone with the coconut extract, sugar and vanilla
filling until smooth. Transfer the filling to a piping bag with a large
star-shaped nozzle and pipe it on top of the cooled cupcakes.