Lemon meringue pie
Question of the Week from the SF Chronicle Food & Wine newsletter (e-mailed 11/12/09):
Q: What would cause the lemon filling in a lemon meringue to be "watery"?
A: There could be a few things at play here. In some cases, it may be humidity that causes the pie to weep. Also, if there is cornstarch in the filling, it can cause the filling to become watery if it is overcooked.
It's also important to add the meringue topping while the lemon filling is still hot, so the steam goes all the way through the meringue and escapes during baking. If it's cold, the steam doesn't make it all the way through the meringue and tends to collect under the surface, causing a wet layer.