Preheat oven to 350°F (175°C). Line a 10x15-inch jelly roll pan with parchment paper and lightly grease.

Beat egg yolks with 1/2 cup sugar for 3 minutes until thick and pale. Add cocoa powder, vanilla, and salt, mixing until combined.

In separate bowl, beat egg whites to soft peaks, gradually add remaining 1/4 cup sugar, beating to stiff peaks.

Fold one-third egg whites into chocolate mixture, then alternate folding remaining whites and sifted flour until just combined.

Spread batter evenly in prepared pan. Bake 12-14 minutes until cake springs back when touched.

Dust clean kitchen towel with powdered sugar. Immediately invert hot cake onto towel, remove parchment, and roll cake with towel from short end. Cool completely.

Beat cold heavy cream with powdered sugar and vanilla to stiff peaks. Add mascarpone if using.

Unroll cooled cake, spread filling evenly leaving 1/2-inch border, re-roll without towel. Wrap and refrigerate 2 hours.

For ganache, heat cream until simmering, pour over chocolate chips, let stand 2 minutes, stir until smooth, add butter.

Place chilled roll on wire rack, pour ganache over, spreading evenly. Refrigerate 30 minutes to set, dust with powdered sugar before serving.