Whisk first measure of milk and flour together in a small pot. Place on medium heat and whisk continuously for 2-3 minutes, until a very thick paste forms.
Transfer paste to a large bowl or bowl of your stand mixer. Add remaining doughnut ingredients (except oil). Using the dough hook (or a wooden spoon) knead on low speed, until combined. Continue to knead on low speed for a further 10-12 minutes, until smooth and elastic. If kneading by hand, turn out onto a clean, floured surface and knead for 10-15 minutes, until smooth and elastic.
Form dough into a ball and place in a large, greased bowl. Cover with a damp tea towel and leave to rise in a warm place for 1 hour.
Once dough has risen, pull off a small piece to use as a tester and set aside. Cut dough ball in half, then cut each half into 3 pieces. Weigh each piece to ensure all doughnuts are the same size. Roll each piece of dough into a ball, then roll each ball into a sausage shape, about 15cm long.
Place doughnuts on a baking sheet lined with baking paper. Cover with a damp tea towel and leave to rise in a warm place for a further 30 minutes.
Meanwhile, place raspberries and sugar in a small pot on medium heat. Cook for 3-5 minutes, until combined. Transfer to a bowl and place in the fridge to cool completely.
Place cream in a large bowl and use electric beaters or a whisk to whip to stiff peaks. Keep in fridge, until needed.
Pour oil into a large pot (do not use cast iron) with high sides, until about 5cm deep. Heat on low-medium heat and test the oil temperature with your test piece of dough. If the oil bubbles around the dough, it is ready. You may need to turn your heat down or adjust during frying, so that the doughnuts don't burn.
Start by cooking one doughnut, placing it in the oil very carefully (see tip). Cook for about 3 minutes each side, until golden. Place on a paper towel to drain. Cut a slit down the centre of the doughnut to check that it is cooked through. Cook the rest of your doughnuts, cooking 2-3 at a time. Let cool completely.
To finish, fill a piping bag with whipped cream. Cut down the centre of all your doughnuts, leaving a hinge. Pipe in the cream and drizzle with raspberry coulis. Dust with icing sugar to serve.