Set your oven to 425°F. It is very important that the oven is fully hot before you start baking. A hot oven helps the popovers rise quickly.

Generously grease your popover pan with butter or cooking spray. Make sure to coat the bottoms and the sides well. This prevents the batter from sticking to the pan.

Sift the all-purpose flour into a large mixing bowl. Add the kosher salt and whisk them together. Sifting ensures there are no large lumps in your batter.

In a separate bowl, whisk the room-temperature eggs. Slowly add the milk and the melted butter. Continue whisking until the mixture is pale and fully combined.

Slowly pour the wet ingredients into the dry flour mixture. Whisk gently until the batter is mostly smooth. A few tiny lumps are okay, so do not overmix.

Pour the batter into the prepared popover cups. Fill each cup about halfway or two-thirds full. Do not overfill them, or they might spill over the sides.

Place the pan in the oven for 30 minutes at 425°F. Do not open the oven door during this time. The steam is what makes them grow tall.

Lower the oven temperature to 350°F. Bake for another 5 to 10 minutes until they are deep golden brown. Ensure the outsides feel firm and crisp.

Take the pan out of the oven. Carefully remove each popover and place it on a wire rack. Serve them immediately while they are still warm and steaming.