Position a rack in the center of the oven. Preheat the oven to 400ºF. Grease 12 popover or custard cups. In a large mixing bowl, combine the flour and salt. Stir with a whisk or fork to blend thoroughly. Whisk the milk, eggs, and butter in a small bowl. Make a well in the center of the dry ingredients. Slowly pour the milk mixture into the well while beating the batter. Continue beating for 2-1/2 to 3 minutes, or until the mixture is smooth and free of lumps. Fold in the herbs. Pour into the prepared cups, filling only halfway. Place the cups in the oven on the center rack and immediately lower the heat to 375ºF. Bake for 35 to 45 minutes, or until puffed and browned.