The basic ratio is two eggs per cup of milk/cream and a cup of shredded cheese per pie crust. You'll need more or less of each depending on what other ingredients you add. Pile up the veggies and cheese into the pie crust and then pour the egg/milk mixture over them, pouring slow enough for the liquid to seep through the layers of veggie. Then bake for about 45 minutes.
I usually make two of them, and freeze the second one for later. It is a good way to use up a lot of leftovers.
Here's Alton Brown's Refrigerator Pie recipe as he calls it.
1 cup heavy cream or half-and-half
2 pinches kosher salt
Freshly grated nutmeg
For 1 Refrigerator Pie:
1 frozen 9-inch pie crust
Any one of the following combinations:
Cooked spinach, cheddar cheese, cubed cooked ham
Bacon, Sauteed leeks, and Gruyere cheese
Cooked spinach, canned artichoke hearts, and Parmesan cheese
Roasted chicken, goat cheese, and sun-dried tomatoes
Blanched asparagus and smoked salmon
Port Salut and Spam
In a nonreactive, stainless steel bowl, combine the cream or half-and-half and the eggs. Whisk until combined thoroughly. Add the salt and the nutmeg. Whisk to combine.
Refrigerator Pie Rules:
Heat oven to 350 degrees F. Evenly distribute the pie fillings in the pie crust. Do not overfill the crust with the filling ingredients. Do not pour too much royale into the crust. The eggs will expand upon cooking. Bake the pie until it is firm to the touch like set Jell-O, about 45 minutes. Cool the pie for at least 15 minutes before slicing.