Preheat the oven to 350 degrees Fahrenheit.
Line two 8 inch round cake pans with parchment paper and set aside.
In a large mixing bowl, whisk together the dry ingredients, but leave the sprinkles out for now. Be sure to spoon and level the dry ingredients into your measuring cups. Do not pack them in or the cake will be very dry!
In a second bowl, whisk together the wet ingredients. Be sure to shake the can of coconut milk really well before measuring so the cream and watery part are well combined. If your regular milk was in the fridge, measure it out and then add it to the microwave for about 30 seconds to warm it up a bit.
Add the dry ingredients to the wet ingredients and whisk to combine until smooth.
Add the sprinkles and stir until well incorporated.
Add the batter to the prepared pans, trying to keep them as even as possible. Let the batter sit in the pans for 5 minutes. This is not typical when making a cake, but it really helps with this recipe!
Bake for 33-40 minutes or until a toothpick comes out clean and the center of each cake has a few cracks on the top.
Sometimes a toothpick comes out clean before the center is really done, so try to base it off how the top looks rather than the toothpick test. The color should be uniform and should not look wet at all in the center. All ovens are different, but check at 35 minutes and add just a couple of minutes at a time as needed.
Let cool in the pans for 30 minutes, then flip onto a cooling rack. Peel off the parchment paper and let cool completely.
If you're frosting the same day, I suggest sticking the cakes in the fridge for about an hour to really ensure they're fully cool. If you're frosting the next day, let cool completely at room temperature (a few hours) then wrap tightly but gently in plastic wrap and let sit in the fridge.
To make the buttercream, add the room temperature butter to a bowl or bowl of a stand mixer and beat until creamy.
Add the powdered sugar, one cup at a time, and beat until well combined. Beat in the milk and vanilla until well combined. If you want a thicker frosting, just add a bit more sugar until it reaches your desired consistency.
Add about 1 cup of frosting to the bottom layer, add a handful of sprinkles, top with the second layer, then frost the sides and top of the cake.
To add the sprinkles to the sides, take a handful and carefully throw them add the sides of the cake while the frosting is still wet. If you let it dry, they won't stick, so act quickly. I like to do this over a baking sheet to make clean up easier. It can get messy, but worth it!