1. Place a medium ovenproof skillet, preferably cast iron, in center of oven and preheat oven to 450°F. Let skillet heat at least 20 minutes. Prepare your toppings while you wait.
2. Blend eggs in a blender on high speed until very frothy, about 1 minute. With motor running, gradually stream in milk, then 2 tablespoons butter; blend another 30 seconds. Add flour, cornstarch, salt, and pepper and blend just to combine. 
3. Remove skillet from oven and swirl remaining 1 tablespoon butter in skillet to coat. Immediately pour batter into skillet. Bake the baby until puffed and brown around edges, 20–25 minutes. It will begin to deflate as soon as it comes out. Top as desired.

Toppings
Smoked salmon, crème fraîche, chopped pistachios, sliced spring onions OR flash-cooked asparagus spears, white onion, chopped pistachios, lemon zest, goat cheese, olive oil.