1. Preheat oven to 350°F (175°C). Line a 15×10-inch jelly roll pan with parchment paper, grease, and dust lightly with flour.

2. Prepare a clean kitchen towel by dusting generously with powdered sugar.

3. Sift cake flour, baking powder, and salt together three times.

4. In a large bowl, beat egg yolks with 1/2 cup sugar on high speed for 3-4 minutes until thick and pale yellow.

5. In a separate clean bowl, whip egg whites until foamy, gradually add remaining 1/4 cup sugar, and beat until stiff peaks form.

6. Gently fold one-third of egg whites into yolk mixture, then sift flour mixture over top and fold gently.

7. Add remaining egg whites and fold just until no white streaks remain.

8. Pour batter into prepared pan and spread evenly. Bake 12-15 minutes until cake springs back when touched.

9. Immediately invert onto sugared towel, peel off parchment, and roll cake with towel from short end while still warm.

10. Cool completely on wire rack, about 1 hour.

11. Prepare coffee soak by combining espresso, sugar, and vanilla, stirring until sugar dissolves.

12. Beat cold heavy cream until soft peaks form. In another bowl, beat mascarpone, powdered sugar, vanilla, and espresso powder until smooth.

13. Fold whipped cream into mascarpone mixture in three additions.

14. Carefully unroll cooled cake and brush with half the coffee soak.

15. Spread 2/3 of mascarpone cream over cake, leaving 1-inch border on far edge.

16. Re-roll cake without towel, place seam-side down on serving platter.

17. Spread remaining mascarpone cream over outside, creating bark texture with fork.

18. Refrigerate at least 2 hours or overnight.

19. Just before serving, dust generously with cocoa powder and garnish with chocolate shavings.