
Preheat the oven to 400 degrees F. Grease one 9×13-inch baking dish or two 8-inch pie plates. Set aside.
In a large heavy pot, melt the butter over medium heat. Add the onion and leeks and cook for 5-7 minutes.
Reduce heat to low and stir in the milk, fresh thyme leaves, salt and pepper. Let mixture simmer for about 10 minutes and remove from heat. Pour filling into the prepared baking dish. Set aside.
If you can’t find a leek, it can be omitted or substituted with an additional half of a large onion.
5-6 red potatoes can be substituted. No need to peel, just wash and quarter them.
See notes in blog post about freezing the extra pot pie.