Preheat your oven to 350°F.
Gently place the pie crust into a 9-inch pie plate with shallow sides, crimping the edges for a decorative touch. Prebake the crust for 10 to 12 minutes until it’s just starting to turn golden.
After the crust has cooled for a few minutes, evenly distribute the chopped ham and the mixed cheeses across the bottom of the crust.
Whisk together the milk, eggs, garlic salt, and pepper in a medium bowl. Carefully pour this mixture over the ham and cheeses in the crust, taking care not to overfill.