Preheat the oven to 400°F and line 12 muffin cups with paper liners.
In a large bowl, whisk the egg, milk, and oil together.
Add the flour, baking powder, salt, and dry mustard. Stir to combine.
Fold in the cheddar, broccoli, and scallions.
Divide the batter evenly into muffin cups.
Bake for 18-22 minutes until golden. Let cool slightly and enjoy.
