Preheat the oven to 400°F. While the oven is heating, place a 10" cast iron skillet or 9"x9" baking dish in the oven and allow it to heat.

When the oven is warm, pull the rack with the skillet out, and add the butter to the pan. Push the rack back in, close the oven, and allow the butter to melt and slightly brown.

While the butter melts, combine the eggs, flour, milk, salt, sugar, and vanilla in the basin of a blender, and blend on high until very smooth. You can also combine this with a whisk in a mixing bowl, but we have better results using a traditional blender or immersion blender to get it silky smooth.

Open the oven again, and pull out the rack with the skillet on it. Pour the batter into the melted butter in the skillet and sprinkle with grated nutmeg. Push the rack back into the oven, and bake for 45-50 minutes, or until the top of the pancake is golden brown and bubbly, and the middle looks custardy and buttery. A knife inserted into the center should come out clean.

Remove from oven—it will begin to deflate as soon as you do—and cut and serve immediately topped with your favorite toppings.