Preheat oven to 350° F. Line a 9-inch springform pan with parchment paper and grease with nonstick baking spray or with butter and flour.
In a food processor, process the almonds until finely ground. Set aside. (If using almond flour, skip this step)
In a medium saucepan set over low heat, melt the butter, whipping cream and bittersweet chocolate. Stir frequently and remove from heat when melted and smooth. Set aside to cool for a few minutes, then add the egg yolks one at a time, stirring after each. Stir in the almond extract and salt, if using.
In the bowl of a stand mixer or with a hand-held mixer, beat the egg whites on high speed until foamy. With the mixer still running, slowly add the granulated sugar. Continue to beat the egg whites to stiff peaks.
Carefully fold one third of the egg whites into the chocolate mixture just until combined, followed by another third of the egg whites. Fold in the ground almonds, then fold in the remaining egg whites. Do not over mix.
Pour the batter into the prepared pan and bake until cake surface is puffed and cracked, and center is set (it should barely move when you jiggle the pan), about 40-45 minutes.
Let cool in the pan 30 minutes, then remove the springform pan sides and cool completely to room temperature. For a more fudgy texture, chill in the fridge 1-2 hours before serving. Serve with whipped cream, powdered sugar, berries or other desired toppings.