Pre-heat the oven to 425℉/210℃. Line or generously grease a 12 hole muffin pan.
In a large bowl, stir together the flour, cornmeal, baking powder and baking soda.
Make a well in the middle. Add in the melted butter, eggs, sour cream and milk and whisk until only just combined. (A lumpy batter is fine).
Add a good pinch of salt, the cheese and chopped jalapeños, saving some to top the muffins if desired. Stir together and scoop into the muffin pan.
Bake 18-20 minutes, until golden on top and a skewer inserted comes out clean. Let cool a little before serving. Optional: Brush with more melted butter when serving!
