Whisk malted milk powder with a splash of milk in a saucepan until dissolved.
Add remaining milk and cream then bring the mixture to a simmer.
Whisk egg yolks and caster sugar in a bowl until pale and fluffy.
Pour the warm milk mixture over the eggs while whisking continuously.
Cook the mixture over gentle heat until it thickens enough to coat a spoon.
Freeze the mixture in a container for 4 hours or churn in an ice cream maker.
Mix flour and sugar in a large bowl or free-standing mixer.
Heat 100g of butter with half the milk and whisk in yeast until dissolved.
Pour yeast liquid and remaining milk over the dry ingredients.
Mix or knead the dough for 5 minutes until soft and sticky.
Cover and prove the dough at room temperature for 1 hour until doubled in size.
Grease a 38cm tin and a smaller inner tin with butter.
Melt 150g butter in a roasting tray and mix demerara sugar with cinnamon in another.
Knead the proved dough until smooth and form a large bun shape.
Cut a hole in the centre of the dough and expand it with your fingers.
Dip the dough in melted butter then coat thoroughly with cinnamon sugar.
Place dough in the prepared tin around the inner tin and prove for 45 minutes.
Preheat the oven to 180°C.
Bake for 25-30 minutes until golden-brown and cooked through.
Mix icing sugar and bourbon then drizzle over the finished doughnut.
Serve immediately with a ramekin of ice cream placed in the centre.