Preheat: Position rack in lower third. Heat oven to 450°F. Generously grease popover pan. Place in oven 2-3 minutes while mixing batter.
Blend batter: Combine eggs, milk, flour, melted butter, sugar, and salt in blender. Blend 30 seconds until smooth.
Rest: Let batter rest 10 minutes at room temperature while pan heats.
Fill: Remove hot pan carefully. Fill each cup ¾ full with batter.
Bake high: Bake at 450°F for 15 minutes. Don't open oven door.
Reduce and finish: Lower heat to 350°F. Bake 20 minutes more until deep golden and puffed.
Release steam: Pierce each with knife. Serve immediately.
Make butter: Beat butter until fluffy. Mix in preserves, powdered sugar, and salt.