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 powder, salt and sugar until they're evenly distributed (whisk well).
1 1/2 cup (172g) cake flour, 1 1/2 tsp baking powder, 1/4 tsp fine sea salt, 1 cup (200g) granulated sugar
Add the oil and butter to the dry ingredients and beat together until they're combined.
1/4 cup (60mL) canola oil, 1/4 cup (56g) unsalted butter
Add the egg and vanilla extract and paste and mix until they're fully combined.
1 large egg, 1 tsp pure vanilla extract, 2 tsp vanilla bean paste
Add the sour cream and turn the mixer to low speed, while streaming the milk in. Scrape the edge of the bowl and mix just until the cupcake batter is smooth.
1/2 cup (113g) sour cream, 1/3 cup (80mL) whole milk
Fill each cupcake liner about 2/3-3/4 full, about 50-55 grams of batter per cupcake.* You will have enough batter for about half a cupcake leftover. DO NOT BE TEMPTED to distribute that among the cupcakes, they will sink if they’re overfilled.
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.