Preheat the oven at 160ºC/320ºF conventional oven and line a cupcake tray with 12 cupcake liners.
Sift together the all-purpose flour, baking powder, baking soda and salt and set it aside.
200 g all-purpose flour, ¼ teaspoon baking powder, ¼ teaspoon baking soda, ¼ teaspoon salt
In the bowl of a stand mixer, using the paddle attachment, or in a large bowl with a hand mixer add the butter, and sugar and mix it on medium/high speed for 3 minutes.
70 g butter room temperature, 210 g granulated sugar
Add the egg whites into the mixture and mix on low until combined.
4 egg whites
Scrape down the sides of the bowl and add the flour mixture, continuing on low speed, mixing until just combined.
Finally add the sour cream, vegetable oil and vanilla extract and mix until just combined, make sure not to over mix the cake batter.
150 g sour cream 18%, 2 tablespoon vegetable oil, 1 teaspoon vanilla extract
Using a rubber spatula, give the batter a gentle fold to make sure all of the ingredients have combined.
Divide the cake batter into the 12 cupcake liners and bake them for 23-25 minutes or until a cake tester comes out clean. Let the cakes cool on a cooling rack. After 5 minutes, gently remove the cupcakes from the cupcake tin and let them cool down completely.