1 lb low-fat ricotta (available at most major supermarkets)
1 egg
1-2 oz rum
1/2 tsp. vanilla extract
1 cup sugar
1/2 cup espresso or very strong coffee
1 package savoyardi ("ladyfinger" biscuits, look in Italian groceries, may be in supermarkets)
1/2 tsp. cocoa
Combine first five ingredients in food processor and whiz until smooth (a minute or so). Arrange savoyardi in a single layer in the bottom of a 9x13 pan or casserole. Dribble half the coffee over them. Spoon half the cheese mixture over top, evenly. Repeat with second layer. Dust top with cocoa (I put it in a fine strainer and tap it ever so gently over the top). Refrigerate for at least a day.
This is authentic except for the ricotta; usually mascarpone is used. You can find mascarpone at some supermarkets and at Italian grocers, but it triples the cost and calorie count. Ignore any recipes you see which call for cake, whipped cream, or chocolate.
If you don't have a food processor, you can use a blender with a lot of careful poking with a rubber spatula. If you don't have either, you must use mascarpone, and icing (confectioner's) sugar. You can't get the smooth texture otherwise.
"Tiramisu" means "pick me up!" in Italian.
The basic tiramisu recipe is from Carol Field's book The Italian Baker, with some modifications by me; the idea to use ricotta came from the cuccia recipe in her book Celebrating Italy and from Marcella Hazan's recipe for coffee ricotta cream in Essentials of Classic Italian Cooking.