Preheat oven to 375°F (190°C).
Grease and line a 15x10 inch jelly roll pan with parchment paper.
In a large bowl, beat the eggs and granulated sugar until light and fluffy.
Sift in the flour, cocoa powder, baking powder, and salt. Fold gently to combine.
Spread the batter evenly into the prepared pan.
Bake for 10-12 minutes, until the cake springs back when lightly touched.
Immediately invert the cake onto a clean kitchen towel dusted with powdered sugar.
Carefully peel off the parchment paper.
Starting from the short end, tightly roll up the cake in the towel.
Allow to cool completely.
In a large bowl, beat the heavy cream and powdered sugar until stiff peaks form.
Unroll the cake and spread the whipped cream over the surface.
Reroll the cake without the towel.
In a small saucepan, melt the chocolate and butter together until smooth.
Pour the chocolate glaze over the top of the rolled cake.
Refrigerate until set, about 30 minutes.
