Melt the unsweetened chocolate in a metal bowl set over a saucepan of simmering water, (bain marie) stirring constantly until fully melted.
Remove bowl from heat and whisk in yolks with a fork, the mixture will harden.
Whisk whites with a pinch of salt in a large bowl with an electric mixer at high speed gradually adding the ⅓ cup Lakanto a little at a time, continuing to whisk until whites just hold stiff peaks.
Stir about 1 cup egg whites into chocolate mixture to lighten, then add the mixture to remaining whites, folding gently but thoroughly with a silicone spatula.
Pour into soufflé dish and run the end of your thumb around inside edge of soufflé dish (this will help soufflé rise evenly).
Bake in middle of oven until puffed and crusted on top but still jiggly in center, about 20 minutes. Serve immediately.