Butter or spray a 9-inch (24cm) round cake pan with removable bottom and dust with fine bread crumbs or flour.
Melt 7 ounces semisweet chocolate and 7 ounces unsalted butter together (just like you do for brownies) in the microwave (15-second spurts whisking well after each one) or over a double boiler without touching the water. Reserve.
Have the rest of the ingredients measured and ready. Separate 6 eggs: egg yolks from the egg whites, and place each in a different large clean and dry bowl.
Beat egg whites until you have stiff peaks.
With the same beaters (don’t clean them), beat egg yolks and 1 cup light brown sugar for 3-4 minutes, until light and foamy.
Fold in 1 ½ cups almond flour or ground almonds into the chocolate mixture.
Then add the chocolate mixture to the egg yolks, mixing lightly with a spatula.
Add the egg whites in 3 additions, mixing lightly with a spatula so as not to deflate them much.
Mix all trying to retain as much air as you can. It doesn't matter if it's not 100% mixed. Some streaks of chocolate here and there are ok.
Transfer to the prepared pan and bake for 35-40 minutes, until the top cracks and the surface feels quite firm. It will jiggle a bit in the center.
Let cool completely on a wire rack.
Refrigerate for 4 hours or up to 2 days, well wrapped.
Unmold carefully onto the serving platter, cover with 1 cup dulce de leche or caramel and cover with ½ cup mixed nuts.
Notes
Eggs: when separating the eggs not a single speck of egg yolk is allowed to get into the whites. And the bowl has to be squeaky clean. Otherwise, the egg whites won't rise as they should and the cake will not be as light.Pan size: using the specified pan size is important. If you use a different pan size you will get either a very different final cake. Especially if you use a smaller one, the cake will probably not bake fully in the middle, and the top and bottom will almost burn. If the pan is larger, the cake will be too short and lack a fudgy quality.Storing: this cake can be frozen for up to a month after it has completely cooled. Wrap it well in plastic and then aluminum. Or refrigerate it for a few days before adding the topping and eating it.