Preheat oven to 350F and grease and 8" by 8" square pan.
In a large bowl, whisk together all the dry ingredients. In a separate bowl, whisk the milk, oil, and egg together, pouring this liquid into the dry ingredients. Stir everything together and fold in the jalapeño, cheddar, and scallions.
Pour batter into bowl and bake for 25-30 minutes, until golden brown.
Serve warm or room temperature with softened butter.