In a large bowl, whisk together milk, eggs and 1 Tablespoon melted butter. Add flour, sugar and salt. Stir just until combined, about 30 seconds.
Let mixture sit for 15 minutes while you prepare the pan and preheat the oven.
Adjust one of the oven racks to the bottom third level. Preheat oven to 425° F. Place 1 teaspoon cold butter in each cup of a large popover pan. When the oven is almost fully preheated, place the pan in the oven for exactly 2 minutes so the butter can melt and the pan can get hot.
Once oven is preheated, remove the pan from the oven and immediately divide batter among the cups (each about half to two-thirds full). Place the pan back in the oven and bake the popovers at 425° F for 15 to 20 minutes, then reduce temperature to 350° F and bake for 10 minutes longer. Do not open the oven unless the tops look like they are burning. Place a cookie sheet on the top rack to protect the popovers. Remove from pan immediately and serve hot.
Notes
Muffin pan notes: Place 1/2 teaspoon butter in each cup of a 12-cup muffin tin. Fill each cup half full and bake at 425 F for 15 minutes, then decrease temperature to 350 F and bake for a full 10 to 15 minutes longer (until golden brown).Storing: Popovers are best when eaten when they are recently out of the oven. However, they may be kept in an airtight container for 2 or 3 days (make sure they are completely cooled before storing).Reheating: Preheat oven to 350 F. Place popovers on a baking sheet and reheat for 5 to 10 minutes.Mix-ins: Whisk in 1/2 teaspoon dried thyme or rosemary with the flour and salt. Ground cinnamon or cardamom are also good options.