This ‘set it and forget it’ cake is perfect for the summer months when you don’t want to turn the oven on. And if you forget it in the Instant Pot®, it won’t burn!
Special equipment: kitchen twine; a 6- to 8- quart Instant Pot®. Cook’s Note: Settings may vary on your Instant Pot® depending on the model.
For the cake, coat a 7-inch round cake pan with 3-inch sides with nonstick spray. Line the bottom of the pan with a parchment, coat the paper.
Whisk together the flour, sprinkles, baking powder, baking soda and salt in a medium bowl to combine. *When measuring flour, we spoon it into a dry measuring cup and level off the excess. (Scooping directly from the bag compacts the flour, resulting in dry baked goods.)
Beat the butter in a large bowl with an electric mixer until pale yellow, 2 minutes. Add the confectioners’ sugar and beat on high speed until light and fluffy, 3 to 4 minutes. Add the vanilla and egg, scraping down sides and bottom of the bowl, and continue to beat until creamy, about 2 minutes (the mixture will look curdled but will come back together after it has been beaten for 1 or 2 minutes).
With the mixer on low speed, add the flour mixture in 3 additions, alternating with the sour cream in 2 additions, beginning and ending with the dry ingredients.
Scrape the batter into the prepared pan and smooth the top.
Place two 18-inch pieces of twine criss-crossing one another on a clean work surface. Place the cake pan over the twine, then lay a clean dish towel over the top of the cake pan and tuck the ends under. Take the 2 ends of 1 piece of twine and tie them into a tight knot over the top of the cake pan. Repeat with the remaining twine so that you have two twine handles to support and lift the cake.
Set a rack inside the Instant Pot® and add 2 cups water. Using the twine handles, place the cake inside the pot. Follow the manufacturer’s guide for locking the lid and preparing to cook. Set to pressure cook on high pressure for 40 minutes (see Cook’s Note).
After the pressure cook cycle is complete, follow the manufacturer’s guide for quick release and wait until the quick release cycle is complete. Be careful of any remaining steam and unlock and remove the lid.
Lift the cake out of the pot. Cut the twine and unwrap the cake pan, then transfer to a wire rack. Let the cake cool in the pan, 30 minutes, then invert the cake onto a rack, peel off the parchment and let cool completely.
Invert the cake again so that it is right-side up. Horizontally trim the top dome from the cake with a long serrated knife to create a flat surface. Slice the cake in half horizontally to make 2 layers. (Cake can be baked 1 day ahead.) Wrap tightly in plastic wrap and store at room temperature.
For the buttercream, beat the confectioners’ sugar and butter with an electric mixer on high speed until light and fluffy, about 5 minutes. Scrape in the seeds from the vanilla bean, then add 2 tablespoons cream and continue to beat on high speed for 1 minute more, adding more cream if necessary for a spreadable consistency.
Place 1 cake layer on a cake stand or large plate. Spoon 1 1/2 cups buttercream over the top. Smooth the buttercream to the edge of the cake using an offset spatula or the back of a spoon, creating an even layer. Place another cake layer on top. Spread the remaining buttercream over the top and sides of the cake. Decorate with sprinkles as desired.