Preheat oven to 450 degrees.: You will notice the house begin to warm and the air carries a dry heat that primes the pan to sear the batter instantly, which is crucial for that dramatic puff. Heating the oven thoroughly ensures the skillet becomes extremely hot, giving immediate lift when the batter hits the surface. A mistake here is not allowing enough time for full heat, which leads to a flatter result, so confirm the oven reads 450 before continuing.
Place one tablespoon butter in a 9-12 inch cast iron skillet or 9 inch pie plate. Place in the oven for 5 minutes.: The butter sizzles and foams when it hits the hot pan, smelling nutty and inviting, which helps the edges caramelize. The short time in the oven also melts the butter completely and coats the pan, creating a nonstick surface and a flavor base. Be careful removing the skillet, it will be very hot, and using an oven mitt is essential to avoid burns.
Combine the sugar and cinnamon in a small bowl.: As you stir, the sweet and spicy aroma becomes immediate, and the grains of granulated sugar mingle with the powdery cinnamon to form a topping that will toast in the oven. This pre mix ensures even distribution and prevents clumping when sprinkled, which yields a consistent crust. One pitfall is adding the topping too late, which can cause uneven caramelization, so have it ready before the batter goes in.
Put the flour, milk, eggs, vanilla, and remaining cold butter in a blender. Blend until well blended. Scrape down the sides and blend for about 30 seconds more.: When you blend, the batter becomes silky and lump free, with air incorporated for lift, and the cold butter breaks into tiny morsels that contribute to richness. A good blender pulse followed by a smoother spin gives an even texture, and you will hear the change as the mixture quiets. Avoid over mixing for too long at high speed, which can heat the batter and reduce puff during baking.
Remove the skillet or pan from the oven and swirl the butter all around. Sprinkle with 1/3 of the cinnamon sugar and then pour the batter into the skillet. Place in the oven at 450 degrees for 20 minutes. DO NOT OPEN the oven during this first 20 minutes! After 20 minutes turn the oven down to 350 degrees and bake for another 15-20 minutes until the edges begin to brown.: The batter should have a smooth sheen and an even color, free of streaks of flour or bits of unincorporated butter . Continued blending helps create a uniform emulsion so the pancake sets evenly, and those extra seconds give a light, slightly aerated batter. A common error is leaving lumps which can cause uneven pockets and a bumpy surface once baked.
Remove from oven and let cool for 3-5 minutes. Brush or drizzle with the remaining melted butter, then cover in more cinnamon sugar. Serve immediately.: The sizzling sound as batter meets the hot, buttered skillet confirms a rapid set at the edges, which traps steam and causes the center to puff up dramatically. The initial closed oven stage is critical because any lost steam will deflate the rise, so resist opening the door. When you reduce to 350 after 20 minutes, you will notice the color deepen and the edges tighten into a crisp, lacy frame; that lower heat finishes cooking the center without burning the rim. Opening too early is the most frequent mistake and causes collapse, so be patient and watch the clock.
Remove from oven and let cool for 3-5 minutes. Brush or drizzle with the remaining melted butter, then cover in more cinnamon sugar. Serve immediately.: The first breath of warm cinnamon as you brush on the melted butter is irresistible, and the sugar melts slightly into the hot surface, forming sticky bits that glisten. Letting it rest briefly helps the interior set so it slices cleanly, while the final buttery shower amplifies the aroma and mouthfeel. Serve right away for best texture, as prolonged sitting can soften the crisp edges, which is a common regret when people wait too long.