For the Genoise:
Lightly spray sheet pan with oil spray, top with parchment paper, lightly spray paper as well and set aside.
In a standing mixer, beat eggs, sugar and vanilla, on high, until light and fluffy, a light yellow color, and voluminous. Set mixer speed to lowest setting, and slowly add flour, mixing just until blended. Remove bowl from mixer, and using a spatula lightly mix batter, making sure to scrape bottom to incorporate all flour.
Spread batter evenly in half sheet pan with a light touch so as not to lose volume. Bake for 15 to 20 minutes or until center springs back when lightly touched. Set aside and let cool. Can be made up to 2 days ahead.
For the Tiramisu Cream:
On a double boiler set to medium heat, beat the egg yolks with 8 ounces of the sugar, the espresso and the vanilla extract until light yellow in color and fluffy.
Remove from the heat and add mascarpone in small quantities, making sure each addition is fully incorporated.
Meanwhile, in a large clean bowl, beat the egg whites with half the remaining sugar until ribbons form, then add the remaining sugar, and beat until stiff. Fold into the mascarpone mixture, slowly so as not to lose volume. Cover with plastic wrap and refrigerate overnight to fully set.
To assemble the Tiramisu:
Cut cake using trifle dish or your favorite bowl as a template. Spoon 1/3 of the mascarpone mixture into bottom of dish. Brush top of cake with espresso, flip, brush bottom, place in dish. Add 1/3 of remaining mascarpone. Brush second cake with espresso, flip, brush bottom, place in dish. Cover with remaining mascarpone mixture. Top with whipped cream, chocolate shavings, and dust with cocoa powder.