For the Cake:
Preheat oven to 375 degrees F. Prepare one 10½ x15½ x1 inch Jelly Roll pan; lightly grease the pan or spray with baking spray, line with parchment paper, and then lightly spray with baking spray.
Sprinkle a clean towel with 1/4 cup confectioners’ (powdered) sugar. Set aside to use after the cake is baked. A small kitchen towel that is a little larger than the 15x10 inch pan works well.
In a medium mixing bowl, combine flour, baking powder, and salt; sift or whisk together to mix. Set aside.
In a large bowl of an electric mixer, add the egg yolks and beat 3 to 5 minutes on medium-high speed until the egg yolk foam becomes thick and lemon colored. With the mixer on medium speed, VERY slowly add 1/2 cup of the sugar to the eggs, either one tablespoon at a time, or in a very slow steady stream, taking from 2 to 3 minutes to add all of the sugar, and beating until the eggs and sugar are fully incorporated. Scrape down the sides and bottom of the bowl with a rubber spatula. The mixture will be thick and a pale yellow color. Add the water and vanilla and continue mixing for another 1 minute until well blended.
With the mixer on low speed, gradually add about 1/2 of the flour mixture, mix just until blended, and then add the remaining half, mix just until blended, scraping down the side of the bowl as needed.
In another large mixing bowl and using clean beaters, beat the egg whites with an electric mixer until soft peaks form. Gradually add the remaining 1/4 cup sugar; continue beating until stiff peaks form. Using a balloon type whisk or large rubber spatula, gently fold about 1/4 of the beaten egg whites into the batter to lighten the batter, and then fold the remaining egg whites in.
Spoon the batter into the prepared pan and smooth the surface with the back of a large spoon or large offset spatula. Bake for 12 to 15 minutes or until the top of the cake springs back when lightly touched. Remove from oven, immediately loosen edges of cake from pan and turn the cake over onto the prepared towel. Carefully peel off the parchment paper, and then roll the cake and towel together tightly, starting with the narrow end. Place seam side down on a wire cooling rack to cool completely.
For the Filling:
1 1/2 cups heavy whipping cream, cold
1/2 cup mascarpone
1 teaspoon vanilla
2/3 cup of powdered sugar
Sliced strawberries (about 1 1/2 cup)
*(1/2 cup Strawberry Jam, optional)
To make the filling, whip together the mascarpone, heavy cream, sugar and vanilla until stiff peaks form.
Carefully unroll cooled cake but don’t try to make the cake lie completely flat, the edge should remain curled so that the cake doesn’t split.
Spread whipped cream over the cake and under the curled edge and leaving a 1 1/2 inch border on the far side. Sprinkle strawberries over the whipped cream. Gently re-roll the cake without the towel, starting with the curled end. Place seam side down on a serving plate. Cover and refrigerate at least 2 hours before serving. Dust with additional powdered sugar if desired.
*Note: The original recipe called for 1/2 cup of strawberry jam spread over the cake before spreading on the whipped cream. I didn't have strawberry jam so I left it out but the jam would add a bit more strawberry flavor to the cake so I think I'll add it next time I make this.