• Grease a 10 or 12 cup bundt pan generously with vegetable shortening or butter, then coat it with granulated sugar. Tap out the excess. Set it aside.
• Preheat the oven to 350°F (180°C), or use 325°F (160°C) if your oven is convection.

Caramel

• Place the granulated sugar in a small, heavy-bottom saucepan and set it over medium heat. Stir constantly with a heat-resistant spatula as the sugar begins to melt. Continue stirring until all the sugar has dissolved and the mixture becomes fluid and lightly amber in color, with no remaining granules.
• Remove the pan from the heat (or shut it off). Carefully and slowly pour the water into the melted sugar—it will bubble and steam vigorously, so keep your hands and face back. Once the bubbling settles, return the pan to the stove over medium heat and stir continuously until the hardened sugar dissolves back into the water and you have a thin, smooth caramel.
• Cook just until the crystallized sugar remelts. Remove from the heat and let it cool while you make the chocolate cake batter and the flan.

Chocolate Cake

• In a medium bowl, sift together the flour, cocoa powder, baking powder, and salt. Set aside.
• With a mixer, beat the butter for one minute. Add the granulated sugar and continue beating until the mixture becomes light and fluffy, about 3 more minutes.
• Add the eggs one at a time, mixing well after each addition. Mix in the vanilla extract.
• Add half of the dry ingredient mixture to the bowl and mix to combine.
• Pour in the milk and mix.
• Add the remaining dry ingredients and fold them in with a spatula until the batter is smooth and no streaks of flour remain. Avoid over mixing so the cake stays tender.
• Set aside while you prepare the flan batter.

Flan

• Crack the eggs and pour them in a large bowl through a fine-mesh sieve to strain out any chalazae (the rope-like membrane part) or thicker bits. This ensures the flan stays perfectly smooth and prevents tiny cooked egg specks from appearing in the final texture.
• Add the sweetened condensed milk, flour, vanilla, and heavy cream to the strained eggs. Whisk thoroughly until the mixture is smooth and thin.

To assemble

• Pour the cooled caramel into the bottom of the prepared bundt pan.
• When pouring the chocolate cake batter in, use a cookie scoop or large spoon to transfer it gently and keep it centered. Try not to smear the batter up the sides of the pan—any chocolate smudges on the walls can keep the flan from coming out in an even, clean layer and may cause uneven lines when you unmold the chocoflan.
• Slowly pour the flan batter over the chocolate layer. As the cake bakes, the flan will sink and the chocolate cake will rise. They naturally switch places during baking. That's because the flan mixture is heavier and more liquid, so it sinks, while the chocolate cake batter is lighter and rises as the leavening activates. The cake sets first and the custard sets last, creating the classic “magic” separation that makes chocoflan so unique.
• Bake the chocoflan uncovered, directly on the oven rack, for 35–40 minutes, or until a toothpick inserted into the cake portion comes out clean. The center should look slightly set but still soft.
• Let the cake cool to room temperature in the pan. Cover and refrigerate for at least 6 hours, or overnight so the flan can fully firm up.

To unmold

• To unmold, fill a larger pan with hot water and set the bundt pan in it for 2–3 minutes to loosen the caramel. Place a serving plate on top of the bundt pan, then invert to release the chocoflan.

Storage

• Store it in the fridge, covered, for up to 4 days.