Start by preheating your oven to 350 F. Line the bottom of a 9" springform baking pan with parchment paper (do not grease pan or parchment) and set aside.

Melt the chocolate using a double boiler or microwave. If using a microwave, melt in 30 second increments, stirring after each increment, until chocolate is barely melted. (Even a few small chunks are okay). Stir well to remove any chocolate chunks and to make sure it's smooth. Be careful not to overheat. Add butter into chocolate and stir to combine and let the butter melt. Set aside.

Beat two whole eggs and four whole egg yolks in a medium-sized bowl with 5 1/2 tablespoons granulated sugar, rum extract, and orange zest until well mixed. Gently mix in chocolate mixture. 

In the bowl of a stand mixer with the whisk attachment (or using a hand mixer) whip the four egg whites until foamy. Slowly add in one tablespoon of sugar and continue to whip. Gradually add the remaining two tablespoons sugar and whip until eggs are soft peak stage. 

Add a scoop of the whipped egg whites into the chocolate mixture and fold in to lighten the batter, then fold in the remaining egg whites until combined. Pour into the prepared pan and bake for 30-40 minutes until the cake is risen, cracked, and the center is no longer wobbly. Allow the cake to cool in a wire rack. You'll notice it will sink as it cools. 

Just before serving, remove the cake from the springform pan and place it on a platter. Whip the cream (using a stand mixer or hand mixer). Once the cream begins to stiffen in the bowl, add the sugar and rum extract and whip until soft peaks. Pile into the middle of the cake and dust with cocoa powder (optional, for garnish). Cut into slices and serve. Enjoy!