Line a cupcake or muffin pan with 12 paper liners (see note 3)
Preheat the oven to 356° F / 180° C (160° C fan)
Egg mixture: In a large bowl, beat together eggs, and granulated sugar with an electric mixer on high speed for 4-5 minutes. Beat until the mixture is pale in color.
Add buttermilk or plain yogurt, vegetable oil and vanilla extract. Beat on low speed until just combined, about 30 seconds.
Flour mixture: In a separate bowl, whisk together all-purpose flour, baking powder, baking soda (bicarbonate of soda) and salt.
Combine both: Add the flour mixture to egg mixture, ⅓ at a time, beating on low speed with each addition just until combined.
Add sprinkles: Add the rainbow sprinkles to batter and use a spatula to gently fold (mix) in just until combined.
Scoop the batter evenly into the cupcake liners, filling each about two-thirds full. This gives the batter room to rise without overflowing. (Two-thirds is a bit more than halfway but less than three-quarters of the way to the top)
Bake: Bake for 18 - 20 minutes or until the tops are golden and a skewer inserted into the center comes out clean.
Leave to cool completely before topping with glaze icing.