Preheat your oven to 350°F (175°C) and line a 15x10 inch jelly roll pan with parchment paper.

Whisk together 1 cup of granulated sugar and 4 egg yolks in a large mixing bowl until pale yellow and thickened.

Sift in 1 cup of cocoa powder and 1/2 cup of all-purpose flour, folding gently until just combined.

Whip 4 egg whites until stiff peaks form, then carefully fold into the cocoa mixture.

Pour the batter into the lined pan and bake for 15-20 minutes or until a toothpick comes out clean.

Dust the surface of the cake with powdered sugar, invert onto a clean towel, and roll tightly while warm.

Cool the rolled cake on a wire rack for about 30-45 minutes.

Whip 1 cup of heavy cream with 2 tablespoons of powdered sugar until stiff peaks form.

Unroll the cooled cake, spread the whipped cream filling, and re-roll from the short end.

Prepare the frosting by beating 1 cup of softened unsalted butter until creamy, then mix in powdered sugar and cocoa powder.

Frost the entire surface of the log with chocolate buttercream, creating peaks and swirls.

Use a fork to create a bark-like texture, dust with powdered sugar and decorate as desired.

Slice and serve with hot cocoa or coffee.