Place the milk and melted butter in a bowl and microwave on high for two minutes, or until warm to the touch. In a large mixing bowl, sift together the flour, sugar, salt, and baking powder. In another large bowl, crack the eggs and use an electric mixer to whisk on medium speed for about 3 minutes, until foamy.
Reduce the mixer speed to low and add the warm milk. Gradually add the flour mixture and beat for about 2 minutes. Let the batter rest at room temperature for about 1 hour. For best results, refrigerate the batter overnight, removing it at least 30 minutes before baking.
If using a regular popover pan, preheat the oven to 450°F (232°C). Generously spray the popover pan with nonstick spray. Fill the popover cups almost to the top with batter and place the pan on a cookie sheet. Transfer to the oven and bake for 15 minutes.
Turn the oven down to 375°F (190°C) and bake for an additional 30 to 35 minutes, or until the popovers are golden brown. If using a petite popover pan (strongly recommended), preheat the oven to 350°F (176°C) and bake for about 40 minutes, or until golden brown.
While the popovers are baking, make the Strawberry Butter by placing the ingredients in a bowl and beating until smooth. Then, add the strawberry preserves and continue to beat until fluffy. Serve the popovers with the butter.