Preheat your oven to 425°F. Grease a 12-cup muffin tin or line it with paper liners.
In a large bowl, whisk together the cornmeal, flour, sugar, baking powder, baking soda, and salt.
1 cup yellow cornmeal, 1 cup all-purpose flour, ¼ cup granulated sugar, 1 tablespoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt
In another bowl, whisk together the buttermilk, melted butter, and eggs until well combined.
1 cup buttermilk, ½ cup unsalted butter, 2 large eggs
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix.
Fold in the shredded cheddar cheese, chopped jalapeños, and canned corn (if using) until evenly distributed throughout the batter.
1 cup shredded sharp cheddar cheese, 2 to 3 jalapeños, ½ cup canned corn
Divide the batter evenly among the prepared muffin cups, filling each about 2/3 full.
Bake for 5 minutes in the preheated oven then reduce the heat to 400°F for an additional 10-13 minutes. A toothpick inserted into the center of a muffin should come out clean and the tops of the muffins should be golden brown.
Allow the muffins to cool in the tin for a few minutes before transferring them to a wire rack to cool completely. Serve warm or at room temperature.