Bring the eggs out and let them come to room temperature. To make this go a little faster, separate the eggs’ yolks from the whites. Be very careful doing this, if you break the yolk at all into the egg white, the whites will not form stiff peaks when you need them.
Preheat your grill to 350°F, prepare for indirect grilling.
Grease the sides and bottom of a springform pan thoroughly with butter and set aside.
In a medium saucepan, bring ⅔ cup of water to a simmer. Place a heat proof bowl or another sauce pan over top of this, or use a double boiler. Melt the 3 tbsp. of butter with the chocolate.
In a separate bowl, beat the egg yolks and ½ a cup of sugar together with a mixer on medium speed for about 2 to 3 minutes. Add the espresso powder, salt, vanilla and the melted chocolate. Beat for another minute.
Beat the egg whites in a separate bowl on medium speed until they become foamy. Then add the last of the sugar as you gradually increase the speed on the mixer to high. When stiff peaks have formed, they’re ready. It takes about 5 minutes*.
Gently fold the chocolate mixture into egg whites. Do this in little batches for best results.
Transfer the batter to the prepared cake pan and bake on your grill for 40 minutes or so over indirect heat, until the center is set when you jiggle the pan. You may want to put the springform pan on a baking sheet to catch any batter that leaks before the cake sets.
Remove the cake from the grill and allow to cool.
Serve hot or cold with something delicious like whipped cream or ice cream. I recommend a vanilla, banana or strawberry flavour to go with it.