Break up crackers and chop in food processor. Or place in plastic bag and crush with rolling pin. Mix with margarine and brown sugar. Line bottom of 12-inch springform pan or 13-by-9-by-2-inch casserole. Beat together cream cheese and sugar, at high speed of mixer, for 5 minutes. Beat in eggs, one at a time. Add lemon juice and vanilla. Fold in sour cream. Pour over crust. Bake in preheated 350-degree oven for 1 hour and 15 mintutes. Turn off oven and leave door closed. Leave cheesecake in oven for 2 hours. Cool on rack, then chill. Top with fruit, if desired. Makes 12 to 16 servings.
