Heat the oven to 350°F and put a rack in the center.
Prepare a 9″ spring form pan. Spread 1 tablespoon of the softened butter over the bottom and sides the pan and sprinkle with enough cocoa to lightly coat it. Shake the pan around in a circle to make sure the cocoa powder is evenly coating the entirety of the pan, tossing out any excess.
Place the remaining butter and the chocolate in a large heat proof bowl placed over a pot of simmering water, whisking constantly until shiny, melted, and smooth. Let cool for 2 to 3 minutes until the chocolate is warm, but not hot.
Whisk the egg yolks into the cooled chocolate mixture. Sift in the remaining cocoa powder (I just pass it through a sieve) and salt. Add the vanilla extract and Pernod Classic and whisk until completely combined.
In the bowl of a stand mixer fitted with a whisk attachment, beat the egg whites at low to medium speed for about 15 to 20 seconds until foamy.
Add the cream of tartar and beat at medium speed, for about 1 minute, until the whites form soft peaks.
With the mixer still at medium speed, gradually add the sugar and beat until you’ve created glossy, stiff peaks that stand by themselves when you lift the beaters slightly, 1 to 2 more minutes.
Stir about a quarter of the whipped egg whites into the chocolate mixture to lighten it. Then, with a baking spatula, gently scoop the remaining egg whites into the batter. Fold the egg whites into the chocolate mixture by pulling the spatula toward you from the center of the bowl and then turning the batter over on itself and rotating the bowl as you do so. Continue to do this to incorporate the egg whites without losing volume.