Directions

1. Grease and line a 9" x 13" sheet pan parchment paper. Preheat oven to 350 degrees.
   
2. In a large bowl of an electric mixer with paddle attachment, add 1 cup softened butter, 1 cup caster sugar and 2 teaspoons vanilla. Beat on medium speed until pale and creamy. Add eggs, one at a time, and beat after each addition.
   
3. In a separate bowl, add 2 1/4 cups sifted flour, 3 teaspoons baking powder and pinch of salt, and whisk briefly. Add half of the flour mix and 1 cup room temperature milk and beat on a low speed until combined.
   
4. Add remaining flour mix and 1/4 cup sour cream at room temperature and continue to mix on a low speed until just combined and a thick, creamy cake batter forms. Gently fold in 1/4 cup sprinkles by hand, being careful not to overmix.
   
5. Pour cake batter into prepared pan and smooth the top. Bake for approximately 25-30 minutes or until golden and a skewer inserted in the middle comes out clean. Set on a wire rack to cool completely.
   
6. In a large mixing bowl, add 3/4 cup flour, 1/4 cup caster sugar and cornstarch. Whisk together. Melt 1/4 cup butter in the microwave and pour into mixture, along with 1 teaspoon vanilla, stir briefly. Add 3 tablespoons sprinkles and then stir until it forms wet crumbs that look like wet sand. Pour onto a baking tray lined with parchment paper and spread out into one layer. Place this into the oven after the cake has come out and bake for 10 minutes, then leave to cool completely.
   
7. Place 1 cup room temperature butter in a bowl of an electric mixer. Beat with paddle attachment on medium speed for 1-2 minutes until butter is smooth and creamy. Add 2 teaspoons vanilla and 1 cup powdered sugar. Beat on a low speed to combine, then turn up the speed to medium and mix for 30 seconds.
   
8. Next, add 2 cups powdered sugar, along with 2 tablespoons sour cream. Beat on medium speed until combined. Scrape down the sides of the bowl. Add final cup of powdered sugar, 2 tablespoons milk and 1/8 teaspoon baking powder. Beat on medium speed until frosting is fluffy and creamy.
   
9. Gently remove cooled cake from pan and remove baking paper. Cut out three 6-inch layers using a 6-inch cake ring. You’ll get two whole layers and then two halves. Place a 6-inch cake ring on a plate. Line the inside of the cake ring with a sheet of acetate. Place the two half pieces of cake at the bottom. Press down the cake firmly. If there are any gaps, use extra cake scraps to fill in the holes and press down very firmly to make one even layer.
   
10. In a bowl combine 1/4 cup milk with 1/2 teaspoon vanilla. Spoon 2 tablespoons of the milk soak over the first cake layer. Add a few tablespoons of vanilla buttercream and spread into one layer. Scatter over a handful of cookie crumbs. Add a few extra tablespoons of frosting on top. You don’t need to completely cover the crumbs.
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11. Add another layer of cake and press down firmly. Spoon the rest of the milk soak over the cake layer. Add a few tablespoons of vanilla buttercream and spread into one layer. Scatter over a handful of cookie crumbs. Add a few extra tablespoons of frosting on top.
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12. Add final cake layer and press down firmly. Add remaining buttercream and scatter over cookie crumbs. Place cake in the fridge for at least 1 hour to set.