Preheat oven to 450°F with the rack in the lower third position. Heavily butter the Cuisinart® Popover Pan with the softened butter. Reserve.
Put the 3 tablespoons of butter and milk in a small saucepan set over medium-low heat. Warm until butter has melted, remove and cool to room temperature.
Put the eggs in a medium to large mixing bowl. Add the cooled butter/milk mixture and whisk until well combined. Add the flour and salt and whisk until completely smooth.
Evenly divide the batter among the 6 cups of the buttered popover pan (it will fill each to about ¼ to ⅔ full). Put pan directly on the oven rack and bake for 35 minutes, or until very deeply browned and puffed. Do not open oven door while popovers are baking or they may deflate.
Remove from oven and carefully un-mold from pan. Serve immediately.