Combine flour, cornmeal, baking powder, salt, and sugar together in a large bowl.
Whisk eggs and milk together. Melt butter in cast iron skillet. Add butter to milk and egg mixture, leaving some in pan to coat for baking the cornbread.
Combine wet and dry ingredients. Whisk in jalapenos.
Bake at 375°: 20 minutes in cast iron skillet and 18 minutes in muffin pan.