Preheat the oven to 400º and prepare an 8" pan, grease and lined with parchment paper
Melt the chocolate and butter over a double boiler (or in the microwave on 50% power stirring every 30 seconds, about 3x). Do not overheat the chocolate or it will seize (also, be sure no water gets in the pan or it will seize and be ruined). Set aside.
Lightly beat the eggs in your mixing bowl then continue beating as you warm them over low heat on a double boiler. They should be warm to the touch - don't cook them! Remove from heat and using your standing mixer beat the warmed eggs for 2 minutes, then and add vanilla and sugar. Keep beating 8-10 minutes until triple volume and ribbony (see note).
The eggs and chocolate should be about the same temperature, slightly warm. Blend the two together by slowly folding 1/3 of the egg mixture into the chocolate mixture (to lighten it). Then gradually fold into the remaining egg mixture. Fold, don't stir, until just incorporated. You don't want to overwork it and deflate your eggs.
Gently pour the batter in and bake at 400º for 15 minutes. Do not over bake, it may seem like it’s not done, but it is!
Let cool completely before removing from the pan. Run a knife along the edge and then tip a plate on top and flip it over, remove the parchment. If you are using Erythritol sweetener serve right away, if you are using regular chocolate you will want to let this cool in the fridge for a few hours or overnight.
Serve with freshly whipped cream, raspberries, chocolate shavings and raspberry coulis.