Zwahlen's in Audubon PA is just far enough from Philadelphia that I only head there once or twice a month. Their fresh made and, more importantly, genuine frozen custard is as good as I've had. Two flavors every day, vanilla and chocolate, and one special.
The frozen custard is drawn into serving containers and then scooped to order. All the fruit toppings are fresh. This time of year I almost always end up with a strawberry or a strawberry and blueberry sundae over vanilla custard.
Zwahlen's makes their own chocolate too and a bunch of different designer caramel apples.
Pretty easy to get to from the PA Turnpike. Take the King of Prussia exit, 202 South just a bit to 422 North. Exit onto Trooper Road. Zwahlen's is about two miles on the left, behind the McDonald's.
One warning, they are closed on Sundays.
For those with a GPS:
670 Shannondell Blvd.
Audubon, PA 19403