1. Preheat the Oven and Skillet: Place your 10-inch cast iron skillet into the oven and preheat to 425 F (220 C). Allowing the skillet to heat up with the oven is crucial for achieving that signature puff and crispy crust. You want the skillet to be screaming hot when the batter goes in.

2. Prepare the Batter: While the oven and skillet are heating, combine the flour, milk, eggs, granulated sugar, vanilla extract, and salt in a blender. Blend on high until the mixture is completely smooth and frothy, about 30-60 seconds. Alternatively, you can whisk vigorously by hand in a large bowl until no lumps remain and the mixture is well combined. The frothy texture from blending helps create a lighter, airier pancake.

3. Melt the Butter in the Hot Skillet: Carefully remove the very hot cast iron skillet from the oven using oven mitts. Add the 2 tablespoons of unsalted butter to the hot skillet. Swirl the skillet around to coat the bottom and sides evenly as the butter melts quickly.

4. Pour in the Batter and Add Blueberries: Immediately pour the prepared batter into the hot, buttered skillet. Quickly scatter the blueberries evenly over the top of the batter. Work swiftly, as the skillet loses heat quickly once out of the oven.

5. Bake Until Golden and Puffed: Return the skillet to the preheated oven. Bake for 20-25 minutes, or until the edges are deeply golden brown and dramatically puffed up, and the center is set. The pancake will puff up significantly around the edges, creating a dramatic, bowl-like shape.

6. Serve Immediately: Once baked, carefully remove the skillet from the oven. The pancake will begin to deflate slightly as it cools, which is completely normal. Dust generously with powdered sugar, if desired, and serve immediately with fresh lemon wedges on the side. The tang of the lemon beautifully complements the sweetness of the blueberries and the richness of the pancake.