Preparation

1. Salted butter caramel:
   
   Melt 115 g butter in a frying pan over medium heat. Add the vergeoise sugar. Stir with a wooden spoon until a sandy mixture forms. After another 3 to 5 minutes of cooking, the mixture takes on the appearance of an almost transparent liquid, so add the cream all at once.
   Mix well with a whisk. Continue cooking for 10 min over low heat, stirring occasionally. Add the teaspoon of Guérande fleur de sel and the seeds of a vanilla pod. Leave the caramel to cool.
   Mix 400 g of the caramel with 100 g of butter. Set aside. If you have any caramel left over, you can store it in the fridge for use on vanilla ice cream or to flavour a custard...

2. Chocolate:
   
   Chop the chocolate and cut the butter into small pieces. In a small saucepan, heat 125 ml water over high heat and add 60 g sugar. Lower the heat and leave to reduce to a syrup for around 5 minutes. Remove the saucepan from the heat and add the chopped chocolate, then the butter. Leave to cool. Once at room temperature, add the seeds of a vanilla pod.
   Preheat your oven to 170°C. Prepare a 26 cm cake tin by cutting out a disk of parchment paper for the base. Butter the edges. Prepare a bain-marie with a much larger pan, half-filled with water.

3. The cake:
   
   Beat the eggs with 75 g sugar for 10 to 15 min: the volume should double. Pour half the mixture into another large bowl. In one of the 2 bowls, gently add the 400 g butterscotch. In the 2nd, add the melted chocolate.
   Pour about a third of the chocolate mixture into your mold, followed by a third of the butterscotch mixture. Repeat 3 times to give your cake a slightly marbled appearance.
   Alternatively, for a "bi-color" cake, pour all the chocolate mixture first, then the caramel mixture on top.
   Bake for 40 min in a bain-marie. Leave to cool for several hours or overnight. Before serving, reheat for 5 min in an oven preheated to 200°C for extra softness.

4. Turn out the cake and sprinkle each slice with Fleur de Sel de Guérande. It adds a touch of crunch and enhances the sweet flavors!