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1
Preheat oven to 350 degrees F.
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2
Butter a half sheet pan (17x12 inches), then line with parchment paper.
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3
Butter the paper and sides of pan and dust with cocoa powder.
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4
In a medium-sized, heat-proof bowl, set over a saucepan of simmering water, whisk together the eggs, sugar, and 2 tablespoons of cocoa powder.
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5
Whisk almost constantly until mixture is warm to the touch.
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6
Remove from heat, and with an electric mixer, beat on high for several minutes until the mixture is smooth, falls in ribbons, and is cool to the touch.
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7
Stir in vanilla.
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8
Combine the rest of the cocoa powder, flour, and salt in small bowl, and fold a third of it into the egg and sugar mixture.
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9
Fold the next third in until well incorporated, followed by the melted butter, and the last third of the flour mixture.
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10
The batter should now fall in thick ribbons.
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11
Spread evenly into prepared pan and bake for 10 minutes, or until cake springs back when touched.
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12
Allow cake to cool.
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13
Meanwhile, beat together the butter, shortening, vanilla, marshmallow fluff, salt and powdered sugar until smooth.
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14
When cake is almost fully cooled, spread the filling evenly over it.
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15
Carefully roll the cake up, being careful not to break the cake or squish out the filling (this will probably happen, so don't panic.
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16
When it is rolled up, place in the freezer to set for about 20 minutes.
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17
Remove the rolls from the freezer and cut the roll into equal slices 1/2-1 inch wide.
