Place milk and melted butter in a bowl and microwave on high for two minutes, or warm to touch. Sift flour, sugar, salt and baking powder in a large mixing bowl. Crack eggs in another large bowl with an electric mixer and whisk on medium for about 3 minutes, until foamy.
Turn down mixer speed to low and add warm milk. Gradually add flour mixture and beat for about 2 minutes. Let 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 you are using a regular popovers pan, preheat oven to 450°F (232°C). Spray popover pan generously with nonstick spray. Fill popover cups almost to the top with batter and place popover pan on cookie sheet. Transfer to oven and bake for 15 minutes.
Turn oven down to 375°F (190°C) and bake for 30 to 35 minutes longer, until popovers are golden brown. If you are using the petite popover pan (strongly recommended), preheat the oven to 350°F (176°C) and bake for about 40 minutes, or until popovers are golden brown.
While baking, make the Strawberry Butter by placing the ingredients in a bowl and beat until smooth, add the strawberry preserves and beat until fluffy. Serve the popovers with the butter.