Pour the sugar and the cold water into a saucepan over medium heat. Leave the sugar to completely melt and dissolve it into a golden-brown syrup.
Soak the gelatin sheets in cold water for 5 minutes.
Add hot water, stir for 20 seconds, and remove the syrup from the heat.
Remove the gelatin sheets from the water, add to the syrup, and stir until the gelatin completely melts and dissolves into the syrup.
Pour the syrup onto a baking tin, let it cool down, and then refrigerate for 30 minutes.
How to Make Flan
In a large mixing bowl, add the eggs, sugar, milk, whipping cream, and water. Whisk together until everything is thoroughly combined.
Pour and sieve the custard mixture into the caramel-coated tin.
How to Make the Cake
In two large mixing bowls, separate two egg yolks and white.
Add milk, and melted butter over the egg yolks, whisk together, and then sieve the cake flour and whisk again until everything is fully combined.
Beat the egg whites on medium-low speed with a hand mixer until foamy around 2 minutes, then add sugar and cream of tartar, increase the speed, and beat until they get a stiff peak around 4 minutes.
Carefully fold the beaten whites into the cake mixture.
Pour the cake mixture over the custard mixture.
Place the tin in a large baking tray, pour hot water, and bake for 20 minutes @150c with the fan.
Remove the tray from the oven, cover the top of the tin with aluminium foil, and then bake for 30 minutes @140c with the fan.
Remove the tray from the oven, then lift the tin out of the water bath. Remove the aluminium foil and let it cool to room temperature.
Once it's cooled, refrigerate for 4 hours or overnight.
Place a platter on top of the flan, flip it over, and carefully lift off the baking tin.
Slice the flan and serve.
Notes
Avoid Over-Stirring: When melting sugar for caramel, don’t stir too much, or it may turn grainy. Instead, gently swirl the pan to help it melt evenly.Careful with Gelatin: Make sure the gelatin is fully soaked and dissolved when you add it to the syrup. Just be sure the syrup isn’t boiling, as high heat can ruin its ability to set.Mix Gently: Don’t over-whisk the custard, too much air can create bubbles and mess up the texture.Water Bath: A water bath (bain-marie) ensures even cooking for a smooth, creamy flan. The water should come about halfway up the sides of the dish.Separate Eggs Carefully: Be sure no yolk gets into the egg whites, or they won’t whip properly. Also, use a clean, grease-free bowl for beating.Fold Gently: When folding whipped egg whites into the yolk mixture, do it carefully to keep the air bubbles intact. This helps make the cake light and airy.Aluminum Foil: Cover the cake with foil partway through baking to prevent it from browning too much on top.Chill Time: Let the flan cake chill for at least 4 hours (or better yet, overnight) before unmolding. This helps it set and makes flipping easier.Unmolding: Before flipping, run a knife around the edges to loosen the flan. The caramel will naturally drizzle over it when you flip it out.