Preheat the oven to 425ºF with the oven rack in the center position. Grate the cheese and chop the thyme, setting them aside for later.
In a cast iron skillet over medium heat, sauté the diced bacon until well browned. Remove the bacon with a slotted spoon and set it aside. Leave about 2 tablespoons of bacon fat in the skillet, then place the skillet in the oven to heat while you prepare the batter.
In a small bowl, whisk together the flour, cornstarch, salt, and pepper.
In a blender, blend the eggs on high for 1 minute. Add the milk and 2 tablespoons of melted butter and blend to combine. Add the dry ingredients and blend briefly until mixed.
Carefully remove the hot skillet from the oven and add the remaining butter to the bacon fat. Pour the batter into the skillet, then top with bacon, cheese, and thyme. Return to the oven and bake for 20 minutes, until puffed and golden.
This dish is a variation of a baked pancake, which is often topped with sweet ingredients like berries, fruit compotes, whipped cream, or maple syrup. I make mine savory, as an alternative to Yorkshire pudding or popovers.
The batter is poured into a piping-hot skillet with hot, melted fat. As it bakes, it climbs the edges of the cast iron, forming a showstopping poof. Serve it straight from the oven, right in the cast iron pan for maximum effect.