Have eggs and butter at room temperature. Cream butter; add powdered sugar, beat with electric mixer until fluffy. Add eggs, one at a time; beat well after each addition. Sift flour 3 times; fill empty sugar carton with flour, and add gradually to batter. Add flavoring and juice and mix well. Bake in a greased and floured bundt pan or 10-inch tube pan at 325° for 1½ hours. Cool 4 minutes, then invert pan.
Bring 1 cup berry juice to boil. Combine cornstarch and sugar; mix in a little of the juice, then stir into the boiling juice. Stir and boil 1 minute. Add lemon juice and butter. Remove from heat; stir in berries. Serve over cake, either warm or cool.