Preheat oven to 400°F. Grease a 15x10x1-inch jelly roll pan. Line bottom with parchment paper; grease paper.

Sift flour, baking powder and salt onto parchment paper and set aside.

In a mixer bowl, beat egg yolks on high speed until thick and lemon colored. Slowly add sugar then beat an additional 2 minutes after all the sugar is added until thick and light in color. Add in vanilla.

Fold in flour mixture in thirds until completely blended.

In a separate mixer bowl, beat egg whites on high speed until stiff but dry peaks haven't formed.

Fold in egg whites. Spread batter evenly into prepared pan.

Bake for 9 to 11 minutes, or until top springs back when lightly touched.

While cake is baking sift the powdered sugar all over the tea towel.

Remove cake from oven and turn out immediately onto the tea towel  Gently roll the cake in the towel and hold aside, seam side down.

In a medium pot over medium-high heat whisk espresso powder together with sugar and water until mixture comes to a boil.

Reduce heat to medium-low and gently boil, undisturbed, for 1 full minute. Remove pot from heat, cool to room temperature, and store in a covered container, chilled, until ready to use.

Prepare the bottom of the double boiler with simmering water and cover while simmering.

In the top of the double boiler, whisk milk, cornstarch, and sugar together. Heat over medium high heat, whisking constantly, until mixture comes to a boil.

Reduce heat to low then whisk about ½ cup of the mixture into the egg yolks to temper them. Pour egg yolk mixture into pot, whisking to blend. Heat the custard until it reaches 165 F then place pot on top of simmering water and whisk until it heats to just below the boiling point thickens. Custard will still be pourable. Remove from heat, pour into a clean bowl, cover with parchment or film, and cool to room temperature, stirring occasionally. Chill a minimum of 2 hours or overnight.

In a clean bowl whip cream almost until stiff. Add mascarpone to the bowl and mix at lowest speed just until blended. Fold cream into prepared custard.

Carefully unroll the cake from the towel and trim the ends off just one of the short sides.

Brush the cake with the espresso syrup

Use an offset spatula to spread ½ of the Mascarpone filling over the jelly roll.

Gently roll the cake from the trimmed end first and without the tea towel back into a roll. Trim a thin slice off of both ends then place the roll, seam side down, on a serving platter. Cover and chill until ready to serve.

Sift sugar and cocoa together then sift over finished jelly roll just before serving.