Beat your egg whites until they are stiff. I use a whisk, and it takes approximately 5 - 10 minutes to the point where the egg whites are peaky and stiff. Alternately, 3 - 4 minutes in a blender should do the trick. Be sure to have the egg whites completely stiffened, or when you add in your sugar you'll wind up with something resembling marshmallow fluff, and not meringue.
Once the egg whites are stiff, start pouring in your sugar, lemon juice, and vanilla extract, and continuing to whisk.
Pour your mixture into a greased spring form pan with a flat bottom (if you don't have a spring form pan, you can use a round cake pan with a flat bottom), and spread the mixture out evenly. Put this in the oven and cook for one hour.
After an hour, remove from the oven and set on a cooling rack. Once it's completely cooled, remove your meringue from the pan and put it on a plate. When you're ready, pour your topping(s) over the top, cut, and serve.