Preheat oven to 350 degrees F. Line the base of a 9 inch spring form pan with parchment and spray the inside with non-stick spray.

Place a heat safe mixing bowl over a simmering water bath. Melt together ½ cup sugar, ¼ cup honey, chopped chocolate, cocoa, and water. Stir constantly until smooth. Remove the bowl from the heat and allow the mixture to cool slightly.

In a small bowl whisk together yogurt, egg yolks, and vanilla extract so the mixture is slightly frothy and light yellow.

In a new large mixing bowl, whip egg whites with cream of tarter to stiff peaks. Start at low speed and slowly increase speed as the whites thicken and become fluffier. Once the whites have reached the stiff peak stage mix in remaining ¼ cup of sugar about a tablespoon at a time.

Mix egg yolk mixture into cooled chocolate mixture. Then using a rubber spatula begin gently folding the egg whites into the chocolate one scoop at a time. Fold slowly and lightly until egg whites are fully incorporated and batter is all one color.

Turn the batter into the prepared pan and gently smooth the surface.

Bake until the cake is puffy and the center is no longer liquid. Cake is finished when a few moist crumbs stick to a toothpick or cake probe, approximately 30 minutes. Do not over bake. Begin checking after 20 minutes in five minute intervals.

Allow cake to cool completely in the pan. It will collapse slightly as it cools.

Gently remove sides of the spring form and transfer to a cake plate or leave on pan base to serve.

Simply dust with powdered sugar or top with yogurt frosting.