Preheat the oven to 180°C (160°C fan). Line a 12-hole cupcake tray with paper cases. The kitchen will start to feel warm and inviting, but resist the urge to open the door once the heat is on.

Whisk the dry ingredients together. In a large bowl, sift the flour, sugar, baking powder, and salt. Stir them with a whisk until the mixture looks pale and uniform, with no lumps of flour hiding at the bottom.

Add the wet ingredients. Pour in the oil, eggs, milk, and vanilla extract. Whisk gently until the batter is smooth and glossy, with a thick, ribbon-like consistency that falls off the whisk in folds. You should smell the sweet vanilla aroma immediately.

Fold in the sprinkles. Tip in the 60g of sprinkles and use a spatula to fold them through with just 5 or 6 strokes. Stop as soon as you see the colours distributed — overmixing will cause the sprinkles to dissolve and leave grey streaks in the batter. The batter should look like a party in a bowl, with bright dots scattered throughout.

Fill the paper cases. Divide the batter evenly among the 12 cases, filling each about two-thirds full. Use a small ice-cream scoop for even portions — you’ll hear a satisfying plop as each one drops into the case. The batter should be thick enough to hold a slight peak on top.

Bake for 18–20 minutes. Place the tray on the middle rack. Bake until the tops are golden and spring back when lightly pressed with a finger. A skewer inserted into the centre should come out clean or with a few moist crumbs (not wet batter). The smell of vanilla and toasted sugar will fill your kitchen — that’s your cue they’re nearly done.

Cool completely. Transfer the cupcakes to a wire cooling rack. Let them sit for at least 30 minutes — the centres will still be steaming hot, and frosting them now will turn your buttercream into a puddle. The sponges should feel cool to the touch and have a tender, soft crumb.

Make the buttercream. While the cupcakes cool, beat the softened butter in a bowl until pale and fluffy, about 3 minutes. Gradually add the icing sugar, one spoonful at a time, beating well after each addition. Add the milk and vanilla, then beat on high for 1 minute until the frosting is light, airy, and holds a stiff peak when you lift the beater. Friends always ask me for this recipe after trying it at dinner parties.

Frost and decorate. Pipe or spread the buttercream onto the cooled cupcakes. Top with a generous pinch of extra sprinkles. The contrast of the white frosting against the rainbow dots is exactly what a birthday treat should look like — cheerful and unapologetically fun.