Preheat the oven to 350F/177C convection (325F/163C conventional) and line 13 muffin tins with cupcake liners (preferably a light colored pan).
In a medium bowl, whisk together the cake flour, baking soda, baking powder, salt and sugar.
1 1/2 cup (172g) cake flour, 1/4 tsp baking soda, 1/2 tsp baking powder, 1/4 tsp salt, 1 cup (200g) granulated sugar
Add the oil and butter to the dry ingredients and beat together until they're combined. Add the egg whites and vanilla extracts and mix until they're fully combined and then add the milk and sour cream. Gently fold in the sprinkles.
1/4 cup (59mL) canola oil, 1/4 cup (56g) unsalted butter, 2 large (60g) egg whites, 1 tsp pure vanilla extract, 1 tsp artificial vanilla extract, 1/3 cup (78mL) whole milk, 1/2 cup (113g) sour cream, 1/3 cup pastel rainbow sequin sprinkles
Mix just until the cupcake batter is smooth and then fill each cupcake liner about 2/3-3/4 full.* Bake for 16-18 minutes. They are done when you press on the center of the cupcake and it springs back or when a toothpick inserted comes out clean.
Remove them from the oven and let them cool in the cupcake pan for 10 minutes, then move them to a cooling rack. Allow the cupcakes to cool completely before frosting.