Preheat the oven to 400 degrees F. Spray muffin tin with non-stick spray. In a large bowl, combine the cornmeal, flour, baking powder, baking soda, sugar and salt. In another bowl, whisk together the buttermilk, eggs, butter, cheese and diced jalapeno peppers. Add the wet ingredients to the dry ingredients and stir the batter until all ingredients are thoroughly incorporated. Divide the batter into the prepared muffin pan, filling 2/3 of the way full. Place a jalapeno slice on top of each muffin. Bake until golden, about 25 minutes.