3 medium baking potatoes (about 2 lbs.), peeled and thinly sliced
3 tablespoons Cabot Unsalted Butter
1 teaspoon chopped fresh thyme
1 medium onion, finely chopped
3 tablespoons King Arthur Unbleached All-Purpose Flour
1 teaspoon salt
1/2 cup dark beer, such as stout or porter
1 1/2 cups milk
1/2 teaspoon freshly ground black pepper
8 ounces Cabot Sharp Cheddar, shredded (about 2 cups)