In a blender, combine milk, eggs, and the 1 tbsp. of butter until combined. Then add in the flour and salt. Blend until frothy and bubbly.
Let the mixture sit for about 10 minutes
While the mixture is sitting, place muffin tin into oven to warm for 2 minutes, then using a pastry brush, brush the 2 tbsp. of the melted butter in the cavities of the muffin tins. Set aside.
Whiz/blend the batter one more time before pouring the batter evenly into the muffin tins.
Place pan in oven and bake for 15 minutes.
After 15 minutes, WITHOUT opening the oven door, reduce the heat of the oven to 350 °F (177 °C) degrees and bake for 15 more minutes.
After that, you can open your open and remove the popovers. They should feel dry to the touch and have a slightly hollow sound when tapped on.
Turn the popovers onto a drying rack and cut slits in the bottom of each popover to let the steam escape.
Cool enough to be handled and eat immediately. I'll say that they definitely don't taste as good a few hours later and definitely not the next day.
Notes
You can certainly add cheese on top of these popovers before baking them or add some chives or rosemary. It's very interchangeable and versatile. We loved ours with strawberry jam :) Source: The Kitchn