My mother makes a Lemon Meringue Pie every November for my sister. Her birthday is right around Thanksgiving. My sister is 40, so mom has the "no shrinking" down to a science.
Stop the Shrinkage
Prepare your favorite lemon meringue pie recipe. Bake the filling FIRST.
When whipping the egg whites, meringue, add a small of cornstarch, a 1/2 teaspoon to two beaten egg whites. Dissolve the cornstarch first in warm water. The cornstarch helps to thicken and stabilize the meringue so that it seals well. Cornstarch also helps to keep the meringue firm.
Also, undissolved sugar will make a meringue pie weep or shrink. A finer granulated sugar should be used or see that all the sugar is dissolved when beating the egg whites.
Spread the meringue mixture thickly and evenly over the hot filling to the edge of the crust, even over the edge, you can always wipe off the pie dish before putting it in the oven. This seals the filling into the pie and keeps the meringue from SHRINKING!!
Place pie bake in the oven. Make sure the oven isn't too hot. The meringue will brown in an oven that is 260°F to 300°F just fine.