Prepare the Dough: In a large mixing bowl, whisk together the plain flour, caster sugar, baking powder, bicarbonate of soda, and salt. The mixture should look uniform and pale. In a separate bowl, combine the beaten egg, milk, melted butter, and vanilla extract until well blended and the mixture has a light, creamy colour. Pour the wet ingredients into the dry ingredients. Using a wooden spoon or spatula, mix until just combined. The dough will be soft and slightly sticky, but no dry streaks of flour should be visible. Be careful not to overmix, as this can lead to tough doughnuts.

Shape the Doughnuts: Lightly flour a clean work surface. Turn the dough out onto the floured surface and gently pat it down to a thickness of about 1.5 cm. Use a 7-8 cm round cutter (or the rim of a glass) to cut out doughnut shapes. For the holes, use a smaller 2-3 cm cutter. Gather the scraps, gently re-knead them once or twice, and cut out more doughnuts until all the dough is used. You should hear a soft 'thud' as the cutter goes through the dough.

Heat the Oil: Pour the vegetable oil into a large, deep frying pan or a heavy-bottomed pot, ensuring it's at least 5-7 cm deep. Heat the oil over medium heat until it reaches 170-175°C (340-345°F). You can test the oil by dropping a small piece of dough into it; it should sizzle gently and rise to the surface within 10-15 seconds. A thermometer is highly recommended for accuracy. You'll notice a faint, clean frying smell once the oil is ready.

Fry the Doughnuts: Carefully place 2-3 doughnuts into the hot oil, ensuring not to overcrowd the pan. They should float and have space to expand slightly. Fry for 1-2 minutes on each side until they turn a beautiful golden-brown colour and sound hollow when lightly tapped. Use a slotted spoon or tongs to carefully flip them. Once cooked, lift them out and place them on a wire rack set over a baking tray to drain any excess oil. Continue frying in batches until all doughnuts are cooked.

Prepare the Chocolate Glaze: While the doughnuts are cooling, melt the chopped dark chocolate and 2 tablespoons of butter in a heatproof bowl set over a saucepan of simmering water (bain-marie method), or in a microwave in 30-second bursts, stirring in between. Stir until the chocolate is smooth, glossy, and has a rich, deep brown colour, and smells wonderfully sweet and earthy.

Glaze and Decorate: Once the doughnuts are cool enough to handle but still slightly warm, dip the top half of each doughnut into the melted chocolate, allowing any excess to drip off. Place them back on the wire rack. If desired, immediately sprinkle with icing sugar, sprinkles, or chopped nuts before the chocolate sets. The chocolate will start to firm up, creating a slightly shiny, smooth coating. After testing this recipe five times, I finally got the cooling and glazing timing just right for that perfect chocolate shell! My kids absolutely devour this every time I make it, especially when they get to add their own sprinkles.