Bring coffee to a boil and pour over chocolate. Mix until smooth.
In a mixer with the whip attachment, place the egg yolks and 1/2 cup (118ml) of sugar. Whip until yolks are thick and light yellow in color.
Transfer this mixture into a medium mixing bowl.
Clean mixer bowl and whip attachment.
Fold chocolate mixture into egg yolk mixture.
In a clean mixer whip egg whites to soft moist peaks. Add the 4 Tablespoons (60ml) of sugar to the whites while whipping.
Line a half sheet pan with parchment paper and paint with melted butter.
Fold whites into the chocolate egg yolk mixture.
Scrape into prepared pan and slide into a 350’F (177’C) oven for 18-20 minutes.
Allow to cool for 1 hour.
Whip the 2 cups (473ml) of heavy cream until stiff peaks form.
Fold in the powdered sugar and vanilla.
Loosen cake by running a knife around the pan edges, turn out onto a parchment paper. If the cake is a little sticky, dust parchment with cocoa powder.
Spread whipped cream over cake and roll cake up like a jelly roll or a delicate, expensive rug, using the parchment to help the rolling. Wrap in heavy duty foil.
Transfer to a pan and place in refrigerator or freezer until firm.