Step 1

Preheat the oven to 350°F. In a large mixing bowl, combine the sugar, vegetable oil, butter, eggs. egg yolks and vanilla extract. Beat on medium speed until the eggs and oil are well incorporated and the batter is lighter in color, about 2 minutes. Scrape down the bowl as needed. Next mix in the sour cream and beat until well combined.

Step 2

In a separate bowl, combine the remaining dry ingredients. Alternate adding half the dry ingredients and half the buttermilk at a time and mix just until the flour starts to incorporate. Then add remaining dry ingredients and buttermilk and beat until well combined. Use a spatula to scrape down the sides of the bowl and stir the batter from the bottom to the top to ensure it’s well mixed. Mix in the sprinkles by hand.

Step 3

Pour the batter in a 9-inch by 13-inch pan and bake at 350°F for 25-30 minutes. Test the cake for doneness by inserting a toothpick into the center of the cake. If the toothpick comes out clean, the cake is done. Remove from the oven and allow to cool completely.

Step 4

Cut the butter into pieces. Using the paddle attachment, whip the butter for 5-7 minutes, scraping down the bowl occasionally, beating until the butter look light in color.

Step 5

Add the powdered sugar and mix on low speed until incorporated into the butter then add the vanilla extract  and heavy cream and mix to combine. Beat for about 60 seconds.

Step 6

Continuing beating on low until the ingredients start to mix together. Increase speed to medium-high and beat for another 3-5 minutes to whip additional air into the frosting. Spread over cooled cake.