Preheat the oven to 350℉ and grease an 18 x 12 inch jelly roll pan. Cover the pan with parchment, grease the parchment and then dust with flour.
Melt the butter and set aside.
Mix the flour, cocoa, and salt and set aside.
Use your whisk attachment in your mixer and whip the eggs and sugar until combined and frothy. Remove your mixing bowl and place it over a pot of simmering water to create a double boiler. Whisk manually until the temperature reaches 110℉ on a candy thermometer. Remove from the heat and return to bowl to the mixer and whisk on medium-high speed until the eggs are pale and have doubled in size. You'll know the mixture is ready when a ribbon of batter falls from the whisk and sits on top of the mixture.
Beat in the vanilla.
Transfer one cup of the batter to the melted butter. Gradually add in the flour and cocoa to the mixing bowl. Stir the butter and cup of batter together then add it back to the mixing bowl and fold in.
Pour the batter into the prepared pan. Tilt the pan to move the batter into the corners. Bake for 20 - 25 minutes; until the edges start to brown and the center is springy.
Prepare a dishtowel with powdered sugar. Sift the sugar evenly over the towel.
When the cake is done, invert the cake on to the towel and remove the parchment paper. Cut the edges off with a serrated knife and roll the cake in the towel from the short end. Set the cake aside to cool, seam side down, while you prepare the seven minute frosting.
Unroll the cake and spread the frosting. Leave a ½ inch unfrosted around the edges. Re-roll the cake without the towel and place it seam side down on a cooling rack set over the jelly roll pan.
Place the Roulade into the fridge to firm up while you prepare the ganache.
Melt the chocolate whisking in the cream. Remove from the heat and add the butter, whisking the entire time until melted, smooth, and glossy.
Slowly pour over the roulade coating the sides. Reserve a ½ cup for garnishing. Place the pan back into the fridge for 30 minutes to firm the chocolate. Remove from the fridge and trim off the edges for a smooth, clean cut.
Remove the roulade using two spatulas and transfer to a serving platter. Re-melt the remaining ganache, dip the marshmallows and place them on top of the roulade. Drizzle with ganache and serve.