Preheat oven to 350°F. Prepare a 9 inch springform pan with parchment paper and grease the sides.

In a medium bowl, combine flour, sugar, cocoa powder, baking soda, baking powder, and salt. Whisk until combined.

In another bowl, mix milk, oil, vanilla extract, and egg white until well combined.

Add dry ingredients to wet and whisk until smooth. Stir in hot water; batter will be thin.

Pour into prepared pan and bake for 12-15 minutes. Cool on a rack.

Reduce oven temperature to 300°F. Prepare water bath setup. Wrap the pan and set aside.

In a large bowl, beat cream cheese, sugar, and cocoa powder until smooth.

Add sour cream and vanilla, mix until combined.

Add melted chocolate gradually, stirring well after each addition.

Add eggs one at a time, mixing slowly. Scrape sides as needed.

Place cake layer at bottom of pan, then pour cheesecake filling over it.

Set pan in water bath and bake for 1 hour 15 minutes. Let it cool slowly.

Refrigerate until firm, about 5-6 hours or overnight.

Once cooled, remove from pan. Whip heavy cream with cocoa, powdered sugar, and vanilla until stiff peaks form.

Pipe whipped cream around edge, decorate with rainbow sprinkles. Refrigerate until serving.