Serve these deliciously-scented popovers right out of the oven.
Heat oven to 450 degrees. Place rack on bottom level. Rub tins with a little oil and set aside.
Heat 1 teaspoon butter in a small saute pan over low heat. Add shallots and cook until soft and transparent, about 5 minutes. Add rosemary and set aside.
Melt 1 1/2 tablespoons butter. Combine with milk, flour, and salt. Beat in eggs one at a time. Add shallots and rosemary.
Heat empty tins for 5 minutes; remove from oven. Divide remaining tablespoon butter among tins and heat until butter sizzles. Divide batter evenly among cups.
Bake for 20 minutes; turn down heat to 350 degrees without opening oven. Bake 20 minutes more. When done, sides should feel crisp and firm. Poke with a sharp knife to release steam; serve immediately.
To make popovers that really pop over, use a popover frame, available in kitchenware shops.