Preheat the oven to 350°F / 175°C. Line a muffin tin with 6 parchment liners.
Add the sugar, flour, baking powder, salt and cubed butter to a medium sized mixing bowl. Use a hand mixer or stand mixer fitted with the paddle attachment to beat the mixture together until the butter has completely combined with the dry ingredients and no large lumps remain.
Whisk together the buttermilk and butterfly pea powder until combined.
Add the buttermilk, oil, egg white, and vanilla to the flour mixture. Whisk the ingredients together just until a cohesive batter has formed.
Distribute the batter evenly between the six liners. Bake for 15-18 min., or until a toothpick inserted in the center of the cupcakes comes out clean.
Two Toned Buttercream
In a medium sized mixing bowl, beat the butter for 1 minute to remove any lumps.
Slowly beat in the powdered sugar until all of it has been used.
Add in the vanilla and 1 tbsp. heavy cream, and beat for an additional minute.
To the remaining 1/2 tbsp. of heavy cream, whisk in the butterfly pea powder.
Split the buttercream in half. To one half, beat in the heavy cream-butterfly pea powder mixture until well combined.
Place each buttercream color into it's own piping bag, and snip off a hole in the top. Then, place those two bags into another piping bag that's fitted with your piping tip of choice.
Once the cupcakes have cooled to room temperature, frost them then serve and enjoy!