Preheat oven to 350F.
Lightly grease a 2-quart oval au gratin dish and set aside.
Combine butter and chopped chocolate in a saucepan; set over low heat and stir until melted. Set aside to cool.
In a small mixing bowl, whisk together the heavy cream and vanilla.
In a separate mixing bowl, combine almond flour, cocoa powder, and salt; whisk until thoroughly incorporated.
Place eggs in the bowl of your stand mixer with the whisk attachment; beat on high speed for 1 minute.
Gradually add in stevia/sweetener and continue to beat on high speed for 5 minutes, or until thick and pale yellow.
Turn mixer speed to low and slowly add in the melted butter and chocolate mixture. Mix until combined.
Gradually add in the almond flour mixture; mix until thoroughly incorporated.
Set the mixer at medium speed and slowly add in the heavy cream mixture; continue to beat for 1 minute, or until thickened.
Transfer the cake batter to previously prepared baking dish.
Grab a sheet pan and pour the hot boiling water in it.
Set the baking dish in the water bath.
Bake for 35 to 40 minutes, or until cake is set, puffed up, and has reached 160F in the center.
Remove from oven and let stand 10 minutes. Cake will deflate.
Scoop out cake into serving bowls.
Optionally, garnish with low carb whipped cream and mint leaves.