1/2 teaspoon kosher salt or 1/4 teaspoon fine sea salt
Freshly ground black pepper
1 1/2 cups all-purpose flour
3 tablespoons unsalted butter, melted
3 tablespoons finely chopped fresh rosemary
Flaky sea salt
Position a rack in the bottom third of the oven and preheat the oven to 450°F. Generously coat a popover pan with baking spray.
In a blender, add eggs, milk, salt, and some pepper and blend to combine. Add the flour and blend for 15 seconds, scraping down the sides of the blender if needed. Add the butter and rosemary and blend just until incorporated.
Fill the popover cups with the batter up to 1/4 inch from the top. Sprinkle with flaky sea salt. Bake for 20 minutes, then lower the oven temperature to 350°F and bake until the popovers have risen and are dark golden brown, 15 to 20 minutes longer. Do not open the oven during the baking process.
Remove the popovers from the oven. Insert a sharp knife twice into the tops of the popovers to release steam. Transfer the popovers to a wire rack. Serve immediately.