Heat oven to 350°F. Beat 4 egg whites in small bowl at high speed, scraping bowl often, until stiff peaks form. Set aside.
Beat 4 egg yolks, 3/4 cup sugar, 1 teaspoon orange zest and 1/2 teaspoon vanilla with wire whisk until thick and lemon-colored. Gradually add butter alternately with flour, mixing well after each addition. Gently stir in egg whites
Pour batter into greased and floured 9-inch round cake pan. Bake for 25 to 30 minutes or until cake begins to pull away from sides of pan. Let stand 15 minutes; remove from pan. Cool completely.
Meanwhile, prepare custard mix according to package directions. Remove from heat. Stir in crème de menthe, 1 teaspoon orange zest and 1/2 teaspoon vanilla. Cover; refrigerate until thickened (about 1 1/2 hours).
Meanwhile, place 1 pint strawberries in 5-cup blender container. Cover; blend on high speed until pureed. Continue blending, gradually adding powdered sugar, until dissolved (1 to 2 minutes). Refrigerate about 1 hour
Tear cake into bite-sized pieces. Place 1/2 of pieces in glass serving bowl. Pour about 1/2 strawberry puree over cake; top with 1/2 custard and 1/2 halved strawberries. Repeat with remaining cake pieces, strawberry puree and custard. Garnish with remaining strawberries, sliced nectarine and mint leaves.
*Substitute 1 (3-ounce) package vanilla cook and serve pudding mix.
**Substitute 1/2 teaspoon mint extract.
Cake, custard and strawberry puree can be prepared the day before. Assemble trifle just before serving.