1. Prepare the Crust:

1. Preheat oven to 350°F (175°C). Line a 15×10-inch jelly roll pan with parchment paper. In a large bowl, beat egg yolks with 1/2 cup sugar until pale and thick. Fold in cocoa powder, vanilla, and salt.
2. In a separate clean bowl, beat egg whites until soft peaks form. Gradually add remaining 1/4 cup sugar, beating until stiff peaks form. Gently fold egg whites into yolk mixture in three additions. Spread evenly into prepared pan.
3. Bake for 12-15 minutes until cake springs back when touched. Immediately turn out onto a clean kitchen towel dusted with cocoa powder. Carefully peel off parchment. Starting from a short end, roll cake and towel together into a log. Let cool completely.
4. For filling, whip heavy cream, mascarpone, powdered sugar, coffee, and peppermint extract until stiff peaks form. Unroll cooled cake, spread filling evenly, and re-roll tightly. Place seam-side down on a serving platter.
5. Frost the outside with a thin layer of melted dark chocolate. Use a fork to create bark-like lines. Pipe vanilla buttercream ‘knots’ and garnish with crushed candy canes and mint.