1. Prepare Cake Layers: Preheat oven to 350°. Beat 1 1/4 cups softened butter and 2 1/4 cups granulated sugar at medium speed with a heavy-duty electric stand mixer until fluffy. Gradually add egg whites, one-third at a time, beating well after each addition.
2. Sift together cake flour and baking powder; gradually add to butter mixture alternately with 1 cup water, beginning and ending with flour mixture. Stir in vanilla and almond extracts. Pour batter into 4 greased and floured 8-inch round cake pans.
3. Bake at 350° for 22 to 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes; remove from pans to wire racks, and cool completely (about 30 minutes).
4. Prepare Strawberry Mousse: Sprinkle gelatin over 1/4 cup water in a small bowl; let stand 5 minutes. Process 2 cups sliced strawberries and 1/4 cup granulated sugar in a blender or food processor until smooth, stopping to scrape down sides as needed. Transfer strawberry mixture to a small saucepan; bring to a boil over medium-high heat. Remove from heat. Add gelatin to strawberry mixture, stirring constantly until gelatin dissolves. Cover and chill until consistency of unbeaten egg whites, stirring occasionally (about 30 minutes).
5. Beat cream at low speed until foamy; increase speed to medium-high, and beat until soft peaks form. Fold whipped cream into strawberry mixture until well blended. Cover and chill 30 minutes or just until mixture is thick enough to hold its shape when mounded.
6. Spread about 1 cup Strawberry Mousse between each cake layer, leaving a 1/4-inch border around edges; cover and chill 3 hours or until mousse is set.
7. Prepare Strawberry Frosting: Beat 3/4 cup softened butter at medium speed 20 seconds or until fluffy. Gradually add powdered sugar and 3/4 cup finely chopped strawberries, beating at low speed until creamy. Spread frosting on top and sides of cake.