Step 1

Preheat oven to 350°F. Coat a 9- inch springform pan with baking spray. Set aside.

Step 2

In a heat-safe bowl set on top of a sauce pot of simmering water, melt the chocolate and butter together until smooth. Remove the bowl from the heat and allow to cool slightly.

Step 3

Separate the eggs, placing the yolks in a large bowl and the whites into the bowl of your stand mixer fitted with the whisk attachment.

Step 4

Using a hand mixer, beat the egg yolks in the large bowl until the are a pale yellow color and thickened, 3-4 minutes. Slowly add in the melted chocolate and mix until combined. Set aside.

Step 5

Add in cream of tartar into the bowl of your stand mixer with the egg whites. Beat the whites on medium-high speed until foamy. Add in the granulated sugar a little bit at a time with the mixer still on medium high speed. Once all the granulated sugar is added, continue mixing egg whites until thick, glossy, and stiff peaks form.

Step 6

Fold the egg whites into the chocolate mixture.

Step 7

Pour the batter into the prepared pan. Place the pan on a larger baking sheet and bake for 40 minutes, or until a toothpick inserted into the center comes out with moist crumbs. Be careful not to over-bake. Cake will puff up and get crackly.

Step 8

Allow the cake to cool in the pan placed on a wire rack.

Step 9

When the cake is completely cooled loosen the cake from the sides using a butter knife. Remove the sides of the springform pan.

Step 10

Dust with powdered sugar or top with whipped cream and raspberries if desired.