Preheat your oven to 425°F (220°C).
Place your cast iron skillet in the oven while it preheats and add 2 tablespoons of cold butter to melt.
In a mixing bowl, whisk together the flour, milk, eggs, vanilla extract, and 1/3 cup of granulated sugar until smooth.
Pour the batter into the seasoned skillet, ensuring it spreads evenly.
Bake for about 20 minutes, or until puffed and golden brown. Do not open the oven door during the first 15 minutes.
While baking, combine the remaining 1/3 cup of sugar with 2 teaspoons of cinnamon in a bowl.
Once done, brush the top with melted butter and sprinkle with cinnamon sugar.
Cut into wedges and serve warm with fresh fruit or maple syrup.
