1. Heat oven to 350 degrees F. Butter and flour 9-1/4 x 5-1/4 x 2-3/4-inch loaf pan.Cake:
2. Into medium-size bowl, sift together flour, baking powder and salt. In large bowl, beat together butter and sugar with electric mixer on medium-high speed until light and creamy, about 3 minutes. Beat in lemon juice and vanilla and lemon extracts. On low speed, beat the flour mixture into the butter mixture, alternating with the milk, in 3 additions, beginning and ending with the flour; continue to beat just until ingredients are combined.
3. Using clean beaters, in a clean medium-size bowl, beat together egg whites and cream of tartar on medium-high speed until firm and glossy peaks form, about 3 minutes. Gently fold beaten whites into the batter in 2 batches. Scrape batter into prepared pan.
4. Bake in 350 degree F oven until cake springs back when touched and toothpick inserted into center comes out dry, 65 to 70 minutes. Let cake cool in pan on wire rack for 15 minutes. Then carefully turn cake out onto wire rack; let cool completely. (If making ahead, wrap cake in plastic wrap; refrigerate until ready to use.)
5. Line 9-1/4 x 5-1/4 x 2-3/4inch loaf pan with plastic wrap, leaving 3- to 4-inch overhang on both long sides. Using serrated knife, cut off top of cake in one piece, slicing across just below top rim of cake. Place cake on a long side; cut off 1/2-inch slice from bottom of cake. Place 1/2-inch slice, cut side up, in bottom of pan. Cut 1/2-inch-thick slice from each long side of cake. Place each slice against each long side of pan, cut side against pan. (You will have a 8-1/2 x 3-1/2 x 1-1/2inch piece of cake left over for snacking.)Raspberry and Strawberry Fillings:
6. In food processor, puree raspberries, 3 tablespoons sugar and 1 tablespoon lemon juice. Force through wire sieve placed over medium-size bowl; discard seeds. Repeat with strawberries and the remaining 3 tablespoons sugar and 1 tablespoon lemon juice, using a separate bowl.
7. In small saucepan, combine water and liqueur. Sprinkle gelatin over top; let stand for 5 minutes to soften. Place saucepan over low heat; heat, stirring constantly, until gelatin is dissolved. Remove from heat and let mixture cool slightly.
8. Stir 2 tablespoons of the gelatin mixture into the raspberry puree and 2 tablespoons of the gelatin mixture into the strawberry puree. There will be a small amount of gelatin mixture leftover; reserve.
9. In a large bowl, with an electric mixer, beat together 1 cup heavy cream and 4 tablespoons confectioners sugar until stiff peaks form. Fold half the beaten cream into each of the berry purees. Refrigerate for 5 to 10 minutes or until each mixture softly mounds when lifted with a spoon.
10. Spoon raspberry mousse into cake-lined pan, spreading evenly to edges. Top with strawberry mousse, spreading level. Top with the remaining top slice of cake, cut side down, pressing down gently. Wrap loaf tightly with plastic overhang and additional wrap, if necessary. Refrigerate 2 hours to firm. Makes 12 servings.