Preheat a fan-forced oven to 160C (320F) or 180C (356F) for a conventional oven. Line a cupcake tin with red foil lined cupcake liners.
In the bowl of a stand mixer fitted with the paddle attachment, add the flour, baking powder, caster sugar and salt. Turn mixer on low speed and allow it to mix for a couple minutes to help everything combine well (alternatively you may do this by sifting the ingredients together). Add the softened butter and let it mix until it resembles a fine sand like texture.
Next, add milk, eggs, yogurt, oil and vanilla extract in a large jug and whisk well.
Add wet ingredients to dry ingredients in a slow and steady stream until no dry ingredients are visible. Scrape down the bowl, add red and pink food gel, and mix for another 20 seconds.
Fill each cupcake liner 3/4 of the way (using an ice cream scoop to transfer the batter into the cupcake liners makes this a quick and easy process otherwise you can use two tablespoons).
Bake for 20-25 min or until a toothpick inserted comes out clean. Allow them to cool completely on a wire cooling rack before frosting.
Core the centre of each cupcake and fill with purple buttercream then blue, green, yellow, orange and pink as demonstrated in the video. Chill for 20 minutes
Fit the end of a piping bag with a Wilton 6B star tip and frost a swirl of the red frosting around the rainbow. Chill in the fridge for 20 minutes.
Use a tsp to carefully sprinkle glitter over the frosting.