Preheat oven to 350°F (175°C) and spray a 9-inch springform pan with non-stick spray.
In a large bowl, mix flour, baking powder, sugar, and salt. Add softened butter using a stand mixer or electric mixer until crumbly.
Gradually add buttermilk, milk, and vanilla extract, mixing on medium speed until fully incorporated.
Fold in 2 cups sprinkles and pour the funfetti cake batter into the prepared pan. Bake for 20-25 minutes, until a toothpick inserted in the center comes out clean.
Let the funfetti cake cool completely.
While the cake is cooling, prepare the cheesecake layer. In a separate bowl, beat the cream cheese until smooth. Gradually add sugar, then mix in eggs one at a time, ensuring each is fully blended.
Add the sour cream, milk, and vanilla extract, mixing until smooth. Gently fold in 1/2 cup sprinkles.
Carefully spread the cheesecake layer over the cooled cake. Bake for 10 minutes, then turn the oven off and leave the door slightly open for 1 hour to prevent cracking.
Let the cheesecake cake cool completely. Chill in the refrigerator for at least 4 hours or overnight before serving.
Serve chilled, garnished with additional sprinkles if desired.