Preheat the oven to 170 °C (fan/convection). Line the bottom of two 20cm/8 inch cake tins with baking parchment and grease the sides. Set aside.
If you haven't already, make the vanilla buttercream frosting and set aside in a medium bowl covered with film wrap.
In the bowl of a stand mixer fitted with the whisk attachment, add the caster sugar, vegetable shortening and vanilla extract. Cream together on high speed for at least 3 minutes or until pale and fluffy. Alternatively use an electric whisk.
300 g caster sugar, 80 g vegetable shortening, 2 teaspoon vanilla extract
In a medium bowl, sieve together the cake flour, cornstarch, baking powder, baking soda and fine sea salt.
300 g cake flour, 4 tablespoon cornstarch, 2 teaspoon baking powder, ¼ teaspoon baking soda, ½ teaspoon fine sea salt
In a measuring jug, whisk together the vegan yoghurt and plant milk until smooth.
200 g vegan yoghurt, 120 ml plant milk
If using a stand mixer, replace the whisk attachment with the paddle/beater attachment and switch to medium speed. Add half of the vegan yoghurt mixture and beat until combined. Add half of the flour mixture and beat again until combined. Repeat with the remaining yoghurt mixture followed by the remaining flour mixture, until you have a smooth, thick batter.
Divide the batter evenly between the two cake pans (I recommend using kitchen scales for this) and smooth the surface with a spatula. Place both cake pans in the oven to bake for 25 minutes.
Remove the cakes. A skewer to the centre should come out clean - if not, place back in the oven for a further 5 minutes. Allow the cakes to cool in their tin for 5 minutes before carefully removing from the tin and leaving to cool fully on a wire cooling rack.
Frost the cakes with the vanilla buttercream (you may not need to use all of the buttercream and there will be plenty left for decorating the top) then sprinkle with the coloured sprinkles before serving.
Note: This recipe uses this frosting recipe. Since this is a separate recipe, the nutritional data displayed above is for the sponge cakes alone, and not for the frosting. The nutritional data for the frosting is displayed separately on the frosting post.