Preheat oven to 325°

Prepare a 7 or 8” spring form pan by lining with buttered parchment (I think you could just butter it if you didn’t have parchment - I used a 7" pan so it would be a bit taller - and that's what I have LOL)

Melt dark chocolate with butter over a double boiler or in short bursts in the microwave, stirring often. Mix in instant espresso powder.

Beat the egg yolks, cream, vanilla and sweetener together and then beat into the chocolate mixture. It may separate, if it does just mix well with a beater to smooth it out. Add espresso powder and vanilla.

With a very clean bowl and mixer beat the egg whites with a small pinch of salt or cream of tartar until stiff peaks form. Fold whites carefully into the chocolate mixture in three even additions.

Pour into prepared pan, smooth very lightly and bake at 325° for about 45 minutes. The cake will not quite set (a toothpick would NOT come out clean!) It will still be a bit jiggly in the center but should look drier on the edges.

Cool and then chill for about 3 or 4 hours. Cut with a hot, sharp knife.

Dust with a light sprinkle of powdered erythritol or Swerve and serve with a few nice fresh berries.

Cover lightly once cooled and store in the refrigerator.