Chocolate Flan Cake (1h 40min)

An ingenious dessert where the two batters swap places as they bake: the cake batter — lighter and leavened — rises, while the flan mixture sinks and settles at the bottom. From a single pan you get two distinct layers: a moist chocolate cake base topped with a dense, silky flan. The secret to nailing the texture is the slow, even cooking of a water bath (bain-marie), which sets the flan without curdling it or creating holes.

Ingredients

Caramel sauce

1 cup granulated sugar
1/2 cup hot water

Flan

1 can (395g) sweetened condensed milk
1 can's worth (395ml) whole milk
3 whole eggs

Chocolate cake

2 whole eggs
1 cup sugar
1/2 cup oil (sunflower or corn)
1/2 cup whole milk
1 cup all-purpose flour
1/2 cup cocoa powder (50% or 70%)
1 tablespoon baking powder

Instructions

Step 1 — Caramel sauce (10 min)

Melt the sugar: In a heavy-bottomed pan, heat the sugar over low heat without stirring. Once it starts melting at the edges, swirl the pan (rather than stirring with a spoon) until you get an even golden caramel — watch closely so it doesn't go too far and turn bitter.
Add the water: Off the heat, carefully pour in the hot water (it will bubble and splatter), then return to low heat, stirring until any sugar lumps dissolve and the sauce thickens slightly.
Coat the pan: Pour the caramel into a tube pan (about 22cm) and swirl to coat the base and sides. Set aside to let the caramel firm up.

Step 2 — Flan (5 min)

Blend the ingredients: In a blender, combine the condensed milk, whole milk and 3 eggs. Blend for about 2 to 3 minutes, until completely smooth. Set aside.

Step 3 — Chocolate cake (10 min)

Mix the wet ingredients: In a bowl, whisk the eggs and sugar together. Add the oil and milk and mix well.
Fold in the dry ingredients: Gradually add the sifted flour and cocoa, stirring until the batter is smooth and lump-free.
Baking powder last: Add the baking powder and fold gently, just until incorporated — don't overmix.

Step 4 — Assemble and bake (1h 10 min)

The magic flip: when assembling, you pour the flan first and the cake batter on top. Because the cake batter is lighter and leavened, it floats and bakes above the flan — which becomes the smooth base once you unmold.

Preheat the oven to 180°C / 350°F.
Assemble: Pour the flan mixture into the caramel-coated pan. Then pour the cake batter gently over it, using the back of a spoon to soften the fall and keep the two from mixing.
Water bath: Cover the pan with foil (shiny side down). Set it inside a larger roasting pan and add very hot water until it reaches halfway up the sides of the pan.
Bake: Bake for about 1 hour to 1 hour 10 minutes. To test, insert a toothpick into the cake portion (near the edge): it should come out clean. The flan layer stays creamy and sets fully in the fridge.

Step 5 — Chill (4 hours)

Cool: Remove from the oven and the water bath and let it cool completely at room temperature.
Refrigerate: Chill for at least 4 hours (overnight is even better).
Unmold: Run a blunt knife around the sides and the central tube. Briefly warm the bottom of the pan over a burner for about 10 seconds to loosen the caramel, cover with a deep plate and flip in one motion.

Tips

The biggest mistake with flan cake is trying to unmold it while still warm. The flan needs the fridge time to set before it can support the weight of the inverted cake.

For a hole-free flan, let the flan mixture rest for 10 minutes and gently tap the pan on the counter before baking to pop any surface air bubbles
Always use already-hot water for the bath: it keeps the oven temperature from dropping and gets the cooking started right away
Too-high heat curdles the flan and creates holes — if your oven runs hot, hold it at 170°C and bake a little longer
The caramel releases more easily if you give the pan a quick warm-up over the flame before flipping; don't overdo it or the caramel melts too much
Swap half the cocoa for 50% chocolate powder if you prefer a sweeter, milder cake