Place a rack in the middle of the oven and preheat the oven to 450°F. Grease a 12-cup metal muffin tin with butter or nonstick cooking spray.  Grease the area between the cups as well as the cups themselves. Make sure the oven is close to temperature before you begin to make the popover batter.

• 4 large eggs, warmed in a cup of hot sink water for 10 minutes before cracking
• 3 tablespoons unsalted butter, melted