In a large bowl, melt the unsweetened chocolate and butter. You can do this in the microwave or over a heated pot of water. Make sure not overheat them as they will burn. Take off heat after its completely melted.
Once it’s fully melted, pour in the heavy cream and natural sweetener. Mix until well incorporated.
In a separate large bowl, add the eggs and beat well with a mixer for 1-2 minutes until texture is nice and fluffy. Add the vanilla extract then whisk some more.
Pour the chocolate mixture into the egg mixture. Whisk with a mixer until fully incorporated.
Preheat oven at 325F.
Grease an 8×8 baking dish with some butter. Pour the chocolate batter into the dish then gently shake the dish to evenly distribute and remove any air.
Place in the preheated oven and bake for 45 minutes.
When done, place on a cooling rack and let it cool for at least 25 minutes.