Preheat oven to 400 degrees F (200 degrees C). Grease a 9x13-inch baking dish.
Beat margarine and sugar together in a large bowl until smooth.
Combine cornmeal, flour, baking powder, and salt in another bowl. Stir eggs and milk in a third bowl.
Pour 1/3 milk mixture and 1/3 flour mixture alternately into margarine mixture; whisk until just mixed. Repeat with remaining ingredients and stir in jalapeno peppers.
Spread mixture evenly into prepared baking pan.
Bake in preheated oven until a toothpick inserted into the center comes out clean, 22 to 26 minutes. Cool in the pan for 10 minutes before slicing.
