• Step 1: Preheat your oven to 400°F (200°C). Grease a 12-cup muffin tin or line it with paper liners.
• Step 2: In a large mixing bowl, whisk together the flour, cornmeal, baking powder, baking soda, and salt.
• Step 3: In a separate bowl, combine the melted butter, buttermilk, eggs, and sugar. Whisk until well incorporated.
• Step 4: Pour the wet ingredients into the dry ingredients and stir just until combined, being careful not to overmix. Fold in the shredded cheddar cheese and chopped jalapeños.
• Step 5: Divide the batter evenly among the prepared muffin cups, filling them about 3/4 full.
• Step 6: Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Allow the muffins to cool in the tin for 5 minutes before transferring them to a wire rack.