Preheat the oven to 400ºF.
In a large bowl, whisk together the flour, milk, eggs, salt and melted butter until the mixture is the consistency of heavy cream.
Place the empty popover pan in the oven for 2 minutes to heat it.
Remove the heated pan and place one cube of the butter in each cup.
Divide the batter into each of the 12 cups, filling each cup until it's half full.
Bake the popovers for 20 minutes.
Reduce the heat to 300ºF and bake the popovers an additional 10 minutes.
Remove the popovers from the oven and serve them immediately with the prepared butter.
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