Preheat convection oven to 160°C (th. 5/6). Spread the hazelnuts on a baking sheet and grill them for 20 minutes. After removal from oven, put in a sieve to eliminate the skin and break up with a rolling pin.

Butter the two 19x9x6.5 cm cake pans, coat with flour then tap to remove extra flour.

Sift the flour and baking powder together and add the grilled crushed hazelnuts.

Set aside.

In a big bowl mix with fingers chopped zests and sugar until the sugar is damp. Add the eggs and beat with a whisk until the mixture is frothy. Add, one after another, cream, rum and fleur de sel. Whip together until all of the ingredients are well mixed. Using a plastic spatula, add by thirds the flour, baking powder and hazelnut mixture to the liquid mixture. Then, add half of the melted, cooled butter followed by the second half.

Pour the batter into the pans and place on a baking sheet and bake for about 60 min. The cakes must be cooked on the edges, split in the middle and golden. A knife inserted into the center of the cake must come out dry and without crumbs (check after 40 min baking time). If cakes brown too quickly, cover with a folded piece of aluminum foil. Remove the cakes from the oven and the pans and place on a cooling rack at room temperature before icing and serving.

If you want to ice the cakes, heat the marmalade in a microwave and put through a sieve. Use a brush to cover the entire surface of the cake (except the bottom) with a thin layer. Let dry before serving (or wrapping up).

Stored in plastic wrap, they can be kept at room temperature for up to one week. You can also wrap and store in a freezer for one month.