Gently warm the milk without letting it boil, then pour it into a bowl. Dissolve the yeast in the milk with 2 tablespoons of warm water. Whisk together, then leave for 15 minutes, or until frothy.
Sift the flour, mixed spice and 1 teaspoon of sea salt into a separate bowl. Tip 150g of it into another bowl, along with 1 tablespoon each of the sugar and the yeast liquid. Mix to a smooth paste and leave to rise for 15 minutes.
When the batter has risen, slowly incorporate small pieces of the butter. Once it is all mixed in, beat the eggs and pour in, then grate in the zest of the orange and stir to combine. Add the rest of the flour and caster sugar and mix well.
Once all the flour is combined, turn out onto a lightly floured surface and knead vigorously for 20 minutes until smooth and no longer sticky (you may prefer to do this in a free-standing mixer with a dough hook, if you have one). Form into a ball, place in a lightly oiled bowl and leave to rise for 1 to 1½ hours, until doubled in size.
Transfer the dough to a floured surface and knock it back by kneading lightly. Divide into 4 and roll each piece into a long sausage. Cut each one in half, then each half into thirds, to give you 24 pieces.
Roll each piece into a ball and pierce a hole in the middle with your thumb. Pop them on a tray lined with greaseproof paper and leave to rise in a warm place for 1 hour, or until doubled in size.
Fill a deep saucepan two-thirds full with vegetable oil and place over a medium heat, until it reaches 160°C (if you don’t have a thermometer, drop in a piece of bread – when it sizzles and turns brown the oil is ready). Stretch the doughnuts back into a ring, then fry them, in batches, for 1 minute on each side, or until golden. Then leave to drain on kitchen paper.
To decorate your doughnuts, roll them in caster sugar or drizzle with melted chocolate and roughly chop freeze-dried berries to sprinkle over. Make a glaze by sieving the icing sugar and whisking in a little water, then brush this over your doughnuts.