Preheat oven to 425°. Place a dab of butter in each cup of a popover pan, or large muffin tin. Place in oven to heat pan and melt butter while you mix the batter. In a medium bowl, whisk together the milk and eggs.
Add the flour and salt and mix just until combined (some lumps will remain). Remove pan from the oven and fill cups ¹/3–½ full. Bake until popovers are tall and puffed, about 30 minutes. Serve immediately—they will begin to deflate right away.