2 sticks (16 tablespoons) unsalted butter, at room temperature
1/4 cup olive oil, or neutral oil
1 1/4 cups granulated sugar
1/4 cup brown sugar
4 large eggs, at room temperature
1 tablespoon pure vanilla extract
1 cup buttermilk
1/2 cup rainbow sprinkles
Vanilla milk
1/3 cup whole milk
1 1/2 teaspoons vanilla extract
Coating and toppings
Two 24-ounce bags good-quality white chocolate chips
1 tablespoon neutral oil, such as vegetable or coconut oil
1/2 cup rainbow confetti sprinkles
1 cup shredded coconut
Shaved chocolate or chopped nuts
Directions
Make the cake: Preheat the oven to 350℉. Spray a 9 x13-inch baking dish with cooking spray. (You can also make the cake in two 9-inch round cake pans.)
In a bowl, whisk together the flour, cornstarch, baking powder, and salt. Set aside.
In a bowl, combine the butter, oil, granulated sugar, and brown sugar. Beat with an electric mixer until light in color and fluffy, 3 to 5 minutes. Add the eggs one at a time, making sure each is fully incorporated before adding the next. Beat in the vanilla.
Add the flour to the batter in 3 additions, alternating with additions of the buttermilk, beginning and ending with flour. Mix just until combined after each addition to avoid overmixing. Gently fold in the sprinkles with a rubber spatula (don’t overmix the sprinkles or they will bleed and streak the batter).
Pour the batter into the prepared pan. Bake, rotating the pan halfway through, until a toothpick inserted into the center of the cake comes out clean, 35 to 40 minutes. Remove the cake from the oven. Let the cake cool completely in the pan.
Meanwhile, make the vanilla milk: Combine the milk and vanilla in a cup. Line a sheet pan with parchment.
Using your hands, crumble the cake to fine crumbs; if some of the edge pieces are hard, make sure to crumble them to small pieces. Pour in the vanilla milk and toss to coat all the crumbs. Using a scoop, carefully pack the cake into the scoop. Release it onto the prepared sheet pan. Repeat with the remaining cake. Refrigerate the cake balls until firm, 30 to 60 minutes.
For the coating and toppings: Melt the white chocolate and oil together either in the microwave or over a double boiler. Whisk until glossy. Place the sprinkles, coconut, and shaved chocolate in separate bowls. With a fork, dip a cake ball into the melted chocolate. Flip it over to cover the bottom. Pick up the ball and tap the fork on the edge of the bowl to release excess chocolate. Drop the cake ball into a topping of choice, carefully spooning some over the ball to coat it completely. Place back on the sheet pan. Repeat until all the balls are coated.
Store the truffles in an airtight container in the refrigerator for up to 2 weeks.