To activate the yeast, combine with slightly warm milk and 50g of the sugar and bring to 38°C (body temperature). Leave in a warm place until it begins to foam

Mix the flour, salt, egg and vanilla in a food mixer with a dough hook attachment

Once the yeast mixture has begun to foam, pour into the flour mix and continue to mix until a soft dough forms

Turn out onto a lightly floured surface and knead for 5 minutes to strengthen the dough

Place the dough in a large plastic container. Spread the thinly sliced butter over the top. Cover the container with a damp tea towel and leave somewhere warm to prove - until doubled in size

Knock back the dough and ensure the butter is evenly mixed in

Separate into doughnut-shaped balls, approximately 20g each, and knead again until smooth and round

Line a baking tray with baking paper. Spread the uncooked doughnuts out on the tray, leaving plenty of room for them to prove. Cover loosely with greased cling film and leave somewhere warm to prove again

Heat a deep fat fryer to 190°C. Once the balls have doubled in size, carefully place them, one by one, into the fryer

Once the underside is golden brown, use a slotted spoon to gently turn over. Continue to fry until evenly coloured

Remove the doughnuts from the oil, shake off any excess. Roll the doughnuts in caster sugar until evenly coated. Leave to cool on a wire rack

Once cool, make an incision in the side of each doughnut and pipe in a small amount of strawberry jam and serve