Purple Velvet Cake with Cream Cheese Frosting {Gonzo Cake} from Baked Occasions

INGREDIENTS

(4-ounce/115 g) package purple yam powder (about 1/2 cup plus 2 tablespoons; see Note)

1/4 cup

canola oil or other vegetable oil

2 1/4 cups

cake flour

3/4 cup

all-purpose flour

1 tbsp

baking powder

1 tsp

baking soda

3/4 tsp

kosher salt

4 oz

(1 stick/115 g) unsalted butter, softened, plus more for the pans

1/4 cup

vegetable shortening, at room temperature

2 cups

granulated sugar

1 tbsp

pure vanilla extract

Blue and red food dyes or gels

large egg whites, at room temperature

3 cups

confectioners' sugar

8 oz

(2 sticks/225 g) unsalted butter, softened

(8-ounce/226-g) packages cream cheese, softened

1 tbsp

plus 1 teaspoon pure vanilla extract (optional)

1/2 tsp

kosher salt