To make the custard, place custard powder in a saucepan. Add 2 tablespoons of the milk and mix until smooth and well combined. Stir in the remaining milk, then add the cream. Cook over a medium heat, stirring constantly for 3-4 minutes or until the mixture boils and thickens. Add the chopped chocolate and mix until smooth. Set aside to cool. Spoon into a piping bag and place in the fridge until required.

Place the warmed milk in a jug. Add the yeast and 3 tablespoons of reserved steeping liquid to the warm milk. Set aside in a warm spot for 5-10 minutes until foaming. Place flour, mixed spice and butter into the bowl of a large food processor (your processor needs to be at least 12 cups). Process until butter is incorporated. With the motor running, pour the milk mixture and egg. Process for 1-2 minutes or until dough has formed a ball and is smooth and elastic. If the dough is a bit to sticky, add more flour, a tablespoon at a time, until it is the right consistency. Add drained sultanas and pulse to combine. Turn onto a floured surface and bring the dough together. Transfer to a lightly greased bowl. cover with a clean tea towel and set aside in a warm spot to rise for 1 hour or until mixture has doubled in size.

Line two trays with baking paper. Turn the dough onto a lightly floured surface and knead for 2 minutes, knocking the air out. Cut the dough into 16 even portions. Roll each portion into a ball and place on the lined tray and flatten slightly, allowing a little room between each to expand. Cover with a tea towel and set aside for 30 minutes to prove.

Place 4 doughnuts in the wire basket of an air fryer and brush with melted butter. Air fry at 180°C for 8 minutes or until crisp and golden. Transfer to a wire rack to cool. Repeat with the remaining doughnuts. (Alternatively, heat a saucepan of vegetable oil to 160°C and deep-fry doughnuts, turning halfway through, for 2-3 minutes or until golden and cooked through).

Cut a small slit into the base of each doughnut. Pipe custard into the slit on the base of each doughnut. Return to the rack, cut side down.

Brush the doughnuts with the remaining reserved steeping liquid and set aside for 5 minutes to set.