Combine the flour, cornmeal, sugar, baking powder, and salt in a large bowl. In a separate bowl, combine the milk, eggs, and butter. With a wooden spoon, stir the wet ingredients into the dry until most of the lumps are dissolved. Don't overmix! Mix in 2 cups of the grated Cheddar, the scallions and jalapenos, and allow the mixture to sit at room temperature for 20 minutes.
Meanwhile, preheat the oven to 350 degrees F. Grease a 9 by 13 by 2-inch baking pan.
Pour the batter into the prepared pan, smooth the top, and sprinkle with the remaining grated Cheddar and extra chopped scallions. Bake for 30 to 35 minutes, or until a toothpick comes out clean. Cool and cut into large squares. Serve warm or at room temperature.
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