Preheat oven to 375°.
Whisk all-purpose flour and cornmeal in a small bowl.
Whisk eggs, sugar, baking powder, salt, and baking soda in a medium bowl until eggs are lightened and smooth, about 30 seconds.
Add ¾ cup buttermilk and half of the dry ingredients and whisk very gently just to barely combine.
Add 2 Tbsp. melted butter, remaining ¾ cup buttermilk, and remaining dry ingredients and whisk just to combine (some lumps are okay). Adding the dry ingredients in two batches, rather than all at once, lessens the risk of over-mixing (which would deflate and toughen the batter).
Using a wooden spoon, fold in the blueberries.
Heat 1 Tbsp. vegetable oil and 2 Tbsp. melted butter in a large oven-safe nonstick skillet (make sure it's at least 8 inches in diameter) over medium-high. We're using a combination of oil and butter because butter adds a lot of flavor but has a low smoke point (which means that it burns easily); mixing it with oil raises that smoke point so that we can have the best of both worlds.
When foaming subsides, scrape in batter and use the back of a spoon to gently nudge it all the way to the edges.
Reduce heat to medium and cook, shaking the pan back and forth occasionally to ensure pancake will eventually slide out freely, until bubbles appear across the surface of the pancake, 5–6 minutes (it will still look quite wet and uncooked in the center, but you should see some browning around the outer edge).
Transfer pan to oven and cook until pancake is puffed and set, 10–12 minutes.
Invert pancake onto a large plate or platter. Admire the crispy, burnished top—its pock-marked surface contains all of your lacey-edged pancake fantasies.
Cut into wedges and serve with room-temperature butter and maple syrup.