Add the plain flour, caster sugar, baking powder and salt to a bowl and mix to combine. With your fingertips, rub the butter into the mixture until it resembles breadcrumbs. Slowly add the milk to the bowl, mixing with a spatula or your hands, until a dough is formed.
Turn the dough out on to a lightly floured work surface and knead until you have a ball that is smooth and not too sticky.
Pour the oil in a large pan and heat until it reaches about 170°C – test this with a thermometer.
While the oil is heating, portion the dough into about
15 balls (about 1 tablespoon of dough each) and roll into mini doughnuts.
Carefully lower the doughnut bites into the oil with a slotted spoon, about 4 or 5 at a time, and fry about 1–2 minutes on each side. Once the doughnuts are a lovely golden colour, transfer them to a tray lined with kitchen paper to soak up any excess oil and then toss each doughnut bite into the caster sugar. Enjoy while still warm.
You can flavour the doughnuts by adding 1⁄2 tsp ground cinnamon, nutmeg or ginger, or 1⁄2 tsp vanilla extract to the dough. You can flavour the sugar coating by adding 1 tsp ground cinnamon.