1/2 cup plus 2 tablespoons pasteurized egg whites (at room temperature)
1/3 cup unsweetened cocoa powder, sifted
How to Make It
Heat oven to 350° with a rack in the lower third. Sift the flour and salt twice; set aside.
To make cake: In a bowl, beat the egg whites with an electric mixer at low speed until foamy (about 2 minutes). Add cream of tartar; beat at medium-high until fluffy and soft peaks form. Gradually add sugar, beating until eggs form a peak when beater is lifted out. Transfer egg whites to a large bowl; sift 1/3 of the flour mixture over the whites. Fold in, using a rubber spatula, scraping up from the bottom of the bowl. Continue to sift and fold in the flour mixture in batches; fold in lemon zest and crushed coffee beans. Transfer mixture to a dry, ungreased 10-inch tube pan. Run a knife through the mixture to remove air bubbles. Bake until top is just golden and a small knife inserted into the cake comes out clean (about 45 minutes). Invert the pan upside down to cool.
Run a knife around the edges and the middle of the pan; remove cake. Cut cake horizontally into thirds; set aside.
Cut 1/2 of the strawberries into thirds or halves, depending on their size. Transfer to a medium bowl and sprinkle with 1 tablespoon granulated sugar; toss and reserve. Chop the remaining strawberries into medium pieces; transfer to a second bowl, then sprinkle with 2 tablespoons granulated sugar and 1 tablespoon of the espresso powder mixture. Toss and reserve.
To make espresso cream: Beat cream cheese with an electric mixer on medium speed (preferably with paddle attachment) until smooth. Beat in powdered sugar at low speed, adding espresso powder and vanilla. Transfer cream cheese mixture to a medium bowl; stir in sour cream by hand. Reserve espresso cream at room temperature.
In a clean bowl, beat the egg whites on low until foamy (about 2 minutes). Increase speed to medium-high, and gradually add the remaining 3 tablespoons granulated sugar. Beat until egg whites are shiny and hold stiff peaks; reserve.
To assemble: Arrange 1/3 of the cut cake in the bottom of a large glass serving dish. Brush the cake well with the espresso powder mixture. Spread 1/3 of the espresso cream over the cake followed by 1/2 of the egg white mixture. Cover with 1/3 of the chopped strawberries and their liquid and 1/3 of the sliced strawberries; dust lightly with cocoa powder. Repeat with a second layer. For top layer, brush final cake layer with remaining espresso powder mixture, and top with remaining espresso cream mixture, chopped and sliced strawberries, and remaining liquid; dust with cocoa powder. (Trifle may be served right away or covered with plastic wrap and refrigerated, up to 6 hours.)