Preheat the oven to 350°F and prepare a 9” springform pan with parchment paper and a light layer of cooking spray. You can also bake this in a regular cake pan lined with parchment paper hanging over the sides.
Melt the chocolate (chopped into small pieces) and butter together in a large bowl in the microwave in short sessions until it melts together completely.
Add the Chambord or flavoring of your choice and stir it in. Set the melted chocolate aside and allow it to cool down to room temperature (but not so cool that it begins to harden).
Whip the egg yolks in a clean mixing bowl with the whisk attachment until they begin to thicken.
Add the 1 ounce of sugar and continue to whip until the mixture reaches the ribbon stage. They will be shiny and drip down on themselves like a ribbon.
Whip the egg whites and salt in a separate mixing bowl on medium speed until very soft foamy peaks begin to form. Pro-tip: Make sure you have a clean mixing bowl and whisk, any fat residue can prevent your meringue from forming.
Gradually add in the 4 ounces of sugar while the whites are whipping.
Continue to whip until the whites reach a smooth soft to medium peak. Do not overwhip the whites, as stiff or “chunky” whites will be more difficult to fold into the chocolate and can also cause the cake to collapse more after baking.
Gently fold the egg yolks into the cooled chocolate mixture with big easy folding movements. I use a bowl scraper for this.
Add a scoop of the egg whites and fold them in to lighten the chocolate mixture.
Using a rubber spatula or bowl scraper, fold in the remaining egg whites until no visible white streaks remain in the batter. Take your time and be gentle, keeping as much volume in the batter as possible.
Pour the batter into the prepared springform pan.
Bake the cake in the center of the oven for about 40 minutes. Try not to disturb the cake while it bakes. Like a souffle, it has a fragile structure that’s vulnerable to temperature changes and vibrations.
Test the center of the cake with a skewer to make sure it comes out with no wet batter on it. Remove from the oven and gently place the cake on a cooling rack for about an hour until completely cool. The cake will begin to deflate, creating a smooth and creamy mousse-like texture inside and gorgeous cracks on top.
Remove the springform pan from the chocolate cake.