Preheat oven to 450 degrees.
Shred the cheddar cheese if you purchased a block of cheddar.
Whisk cornmeal, flour, salt, and baking powder in a large bowl.
Add buttermilk, then whisk in eggs.
Fold in the cheddar cheese and jalapenos.
Scoop into 12 equal portions for smaller muffins. If you want larger, fluffier muffins, scoop into 9 muffins (which I prefer).
Bake until the crust is golden brown about 12-16 minutes depending on how many muffins you scoop. It will take less time for 12 muffins to bake (closer to 12 minutes).