BASE: Beat margarine and sugar until light and fluffy. Blend in egg. Add flour; mix well. Spread dough onto bottom of 9-inch springform pan. Bake at 450, 10 minutes. BODY: Combine cream cheese, sugar and flour, mixing at medium speed on electric mixer until well blended. Add eggs, one at a time, mixing well after each addition. Add peaches and liqueur; mix well. Pour over crust. Bake at 450, 10 minutes. Reduce oven temperature to 250; continue baking 1 hour and 5 minutes. Loosen cake from rim of pan; cool before removing rim of pan. Chill. Garnish with toasted almond slices and additional peach slices, if desired.