Place a medium ovenproof skillet, preferably cast iron, in the center of the oven and preheat oven to 450°. Let the skillet heat for 25 minutes.
Blend eggs in a blender on high speed until very frothy, about 1 minute. With motor running, gradually stream in milk, then 2 Tbsp. melted butter; blend another 30 seconds. Add flour, cornstarch, salt, and pepper and blend just to combine.
Carefully remove the skillet from the oven and swirl the remaining 1 Tbsp. butter in the skillet to coat. Immediately pour batter into the skillet. Bake the pancake until puffed and brown around edges, approximately 20 to 25 minutes. No Peeping for at least 20 minutes! It will begin to deflate as soon as the door is opened.
Top as desired.