For the sauce: In a small saucepan set over low heat, add the sugar and cook to make caramel. In a separate saucepan, heat the cream until just warm. Deglaze the caramel with the cream, standing back to avoid bubbling caramel. Then add the milk and butter. Emulsify the mixture with an immersion blender. Let cool.
For the soil: In the bowl of a food processor add the pretzels, butter and sugar. Pulse to combine. Add the tapioca maltodextrin 1/2 teaspoon at a time, pulsing between additions, to just absorb the extra grease from the butter.
For the cake: Preheat a convection oven set to low fan to 325 degrees F. Warm 1/3 cup of the caramel sauce in a medium saucepan or microwave, then stir in the butter and fleur de sel. Off the heat, stir in the sugar, flour and eggs, in that order, making sure to fully combine each between each addition.
Grease six ramekins and coat with sugar. Divide the cake batter among the prepared ramekins and bake until the cake is cooked on the outside, but still liquid on the inside, 13 minutes 30 seconds (depending on strength of oven), rotating halfway through.
Remove the cakes from the ramekins. Keep warm, top with the soil and serve with ice cream.
The caramel sauce can be made ahead and refrigerated.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.