1. Preheat the oven to 425°F and prepare a 9 x 9 inch baking dish or cast-iron skillet by greasing it with butter or cooking spray. A cast-iron skillet will provide a crispy, golden crust.
2. In a large bowl, combine the dry ingredients: 1 cup yellow cornmeal, 1 cup all-purpose flour, 2 tablespoons sugar, 1 tablespoon baking powder, and ½ teaspoon salt. Whisk to ensure an even mix.
3. In a separate bowl, prepare the wet ingredients by mixing 2 large eggs (lightly beaten), 1 cup buttermilk (or regular milk), and ¼ cup melted butter or vegetable oil. Stir until fully combined.
4. Gradually fold the wet ingredients into the dry ingredients. Mix gently until just combined to avoid overmixing, which can result in dense cornbread.
5. Stir in 1 cup of shredded pepper jack cheese and 2-3 diced jalapeños. Reserve a small handful of cheese and jalapeño slices for topping.
6. Pour the batter into the prepared baking dish or skillet, spreading it evenly. Sprinkle the reserved cheese and jalapeño slices on top for added flavor and decoration.
7. Bake the cornbread in the oven for 25-30 minutes, rotating the dish halfway through for even cooking.
8. Check for doneness by ensuring the top is golden brown, the edges have slightly pulled away from the pan, and a toothpick inserted into the center comes out with moist crumbs. Avoid overbaking to preserve moisture.
9. Remove the cornbread from the oven and let it cool in the pan for about 10 minutes before slicing.
10. Serve the Jalapeno Pepper Jack Cornbread warm, either as a side dish, a snack, or paired with your favorite dips, spreads, or hearty main dishes.