Preheat oven to 450º. Whisk eggs in large mixing bowl until frothy. Add milk, flour, salt, and 2 tablespoons butter; whisk until well blended. Stir in herbs, and transfer to a 1-quart measuring cup.
Use remaining 2 tablespoons butter to grease popover pan; place pan on a baking sheet. Warm pan in oven for 5 minutes. Remove pan from oven, and divide batter equally among popover cups.
Bake at 450º for 13 minutes. (Do not open oven during the first 10 minutes of baking or popovers won't rise properly.) Reduce oven temperature to 350º, and bake 15 to 20 more minutes or until golden brown. Remove from oven, and pierce each with a wooden pick to release steam. Remove from pans, and serve immediately.