Preheat the oven to 350 degrees F. Line a muffin tin with cupcake liners.
In a small bowl, whisk together the flour, baking powder and salt. Set it aside.
Add the butter to the bowl of an electric mixer and beat it until creamy. Add the sugar and beat with the butter on high speed until fluffy, 2 to 3 minutes.
Add in the egg and egg white, mixing well on medium speed until combined. Scrape down the sides of the bowl if needed.
Add in the oil and vanilla extract, beating on medium speed for another minute.
With the mixer on low speed, add in half of the dry ingredients.
Pour in the milk. Add in the other half of the dry ingredients and mix them on medium speed until the batter is combined.
Use a large spatula to stir in the chopped white chocolate.
Fill the liners up 2/3 of the way with the batter. Bake until the tops are set and golden, about 18 to 20 minutes.