What happens in the mould
Heat enters from the outside. Egg proteins coagulate around 65 to 70 degrees and form a structure. At the centre, temperature rises more slowly: pull the mould at the right instant and the middle never reaches the coagulation threshold.
So a fondant is not a filled cake. It is the same batter, baked unevenly.
Why the window is so narrow
Baking continues after the oven — thermal inertia carries the centre up several degrees. A minute too long and the middle sets. A minute short and the cake collapses on turning out.
That is why the same recipe fails from one oven to another: it is not the recipe that varies but the mould's inertia and the real temperature.
The parameters that decide
- Starting temperature of the batter. Batter from the fridge bakes entirely differently from batter at room temperature. The most overlooked variable.
- Mould material. Metal conducts fast, silicone slowly. At equal time the results are unrelated.
- Height rather than diameter. A tall narrow mould protects the centre; a wide one cooks through before the sides hold.
- The chocolate. The richer in cocoa butter, the more fluid the centre stays as it cools.
The most reliable method does not play with time: insert a frozen ganache disc in the centre before baking. It melts while the rest cooks. You leave the lottery, at the cost of a little honesty.
What is really at stake
The fondant is an object of food design before it is a recipe: its value lies in a sequence of perception — the resistance of the crust, then the collapse. The gesture is designed, not only the taste.
our piece on food design sets out what food design does with such sequences.