1. Microwave or heat milk in a saucepan over low heat until just warm to the touch.
2. While milk heats, add eggs and egg white to a large mixing bowl; using an electric mixer, beat eggs on medium speed until pale and frothy (about 3 min.). 
3. Add warm milk to eggs; beat until combined (about 30 sec.).
4. Add warm butter; beat until combined (about 30 sec.). 
5. Reduce speed to low. Add flour and salt; mix just until homogeneous and lightly bubbly (about 30 sec.).
6. Pour batter into a spouted measuring glass or pitcher; let rest at room temperature, covered, for 30 min.
7. Preheat oven to 425°.
8. Spoon ½ tsp. clarified butter into each cup of two 6-cup popover pans. Set pans on a baking sheet in preheated oven; bake for 15 min. 
9. Remove baking sheet with popover pans from oven; carefully pour batter into popover cups, filling each just under ⅔ full. 
10. Return baking sheet with popover pans to oven; bake for 25 min. without opening oven door. 
11. Reduce oven temperature to 325°; continue baking until popovers are golden-brown (14-18 min.). 
12. Remove popover pans from oven; let rest for 1 min.
13. Gently lift popovers from cups; serve immediately.

CLARIFIED BUTTER: Melt 3 tbsp. Kowalski’s Unsalted Butter in a saucepan over low heat; simmer, undisturbed, for 10-15 min. Strain mixture. Discard white milk solids; retain clear yellow clarified butter. Makes about 2 tbsp.