Preheat oven to 350 degrees F and grease 10-12 cup Bundt pan with room-temperature butter. Add caramel sauce to bottom of pan and set aside.

In large bowl or stand mixer, add sugar and butter until light and fluffy, about 2-3 minutes. Add egg and beat until well combined.

In medium bowl, whisk flour, cocoa powder, baking powder, baking soda and salt. Add 1/2 dry ingredients to the wet mixture and mix to combine.

Pour batter into pan over caramel.

In large bowl whisk eggs, condensed milk and vanilla until well combined. Add milk slowly and whisk. Slowly pour flan mixture into cake pan.

Tightly cover pan with foil and place into a large roasting pan. Carefully transfer to oven and add hot water halfway up roasting pan.

Bake 60-70 minutes or until a toothpick inserted into the center comes out clean.

Carefully transfer cake pan to a wire rack and uncover. Allow to cool 1 hour. Refrigerate for 2-3 hours or ideally overnight.

To loosen cake from pan, add to a large bowl of warm water for a few minutes. Place a large plate on top of the cake pan. With 2 hands flip the pan over and slowly release cake from pan.