Fifteen minutes before baking, place the rack in the center of the oven and preheat to 450 degrees. Have a popover pan or muffin tin ready.

Combine the flour, eggs, milk, pesto sauce and salt in a food processor or blender and mix until smooth.

Place the pan or tin in the oven and preheat it for 3 minutes. Remove it from the oven and brush the inside of the cups with the melted butter.

Pour the batter into the cups, filling them almost to the top. (Popover pan will yield six; muffin tin will yield ten.) Bake at 450 degrees for 25 minutes. Reduce the temperature to 375 degrees and continue to bake until the popovers are well browned, 5 to 10 minutes longer. Loosen from the sides of the pan, if necessary, and transfer to a wire rack. Serve immediately.

If you don't have pesto, you can make them plain by using 2 tablespoons of melted butter instead. Or spice up the plain version with 1/2 teaspoon each of curry powder and ginger. There are lots of possibilities.