Preheat the oven to 350° Fahrenheit.
Using an electric hand mixer, in a mixing bowl, mix together the softened butter and sugar.
Then add in an egg and mix for 30 seconds. Add in the vanilla and mix for 30 more seconds.
In a separate bowl, combine the flour, salt, baking powder, and cocoa powder.
Add the dry ingredients to the wet ingredients. Starting on low, gently increase the speed of the stand mixer until the wet and dry ingredients are combined.
Fold in the semi sweet chocolate chips.
Press half of the brownie batter into the bottom of an 8x8 baking dish.
In a microwave safe bowl, microwave the white chocolate chips for one minute and 15 seconds or until the white chocolate chips are melted.
Spread half of the white chocolate chips on the brownie batter. Then use a knife to swirl it into the dough.
Press the remaining brownie batter into the dish.
Then spread the remaining white chocolate on top of the brownie batter and swirl it in.
Bake for 45 minutes or until a toothpick can be inserted into the middle and comes out clean.
Remove from the oven and let cool for 20 minutes. Serve immediately with ice cream or save for later.