Place a rack in the middle of the oven but do not preheat. Brush the inside of a 6-cup popover pan with 1 tablespoon of the melted butter.
In a deep bowl or large measuring cup, whisk together the remaining 1 tablespoon melted butter, the eggs, and the milk until combined.
Add the flour and salt, and stir until just combined; do not overmix—the batter should be slightly lumpy.
Divide the batter among the prepared popover cups, filling each about two-thirds full (approximately 1/3 cup plus 1 tablespoon per cup).
Place the popover pan in the cold oven and immediately set the oven to 375°F (190°C) to preheat with the pan inside.
Bake until the popovers are tall, deep golden brown, and puffy, about 35 to 45 minutes; do not open the oven during the first 30 minutes.
Remove the pan from the oven and immediately make a small slit in the side of each popover with a paring knife to release steam. Cool in the pan for 5 minutes before serving.