Preheat oven to 375°F. Grease a bundt pan and pour in caramel sauce.
In a bowl, cream butter and sugar. Add egg and vanilla.
In another bowl, mix flour, cocoa, baking powder, baking soda.
Alternate adding dry ingredients and milk into butter mixture. Pour into pan.
Blend flan ingredients until smooth. Pour slowly over cake batter.
Place bundt pan in a water bath and bake 60–70 minutes.
Cool to room temp, then chill 4+ hours. Loosen edges and invert to serve.
See full steps with tips & photos → https://theboatshedcafe.com/chocoflan-impossible-cake/