Put muffin mix in a medium bowl.
Add egg and milk and mix until just combined, taking care not to over-mix (it's OK if the batter is a little lumpy).
Heat a griddle or large skillet over medium-low heat and brush lightly with a little butter or cooking spray.
Spoon about 3 Tbsp of batter onto the griddle and cook for 1-2 minutes, until bubbles form on the tops of pancakes. Flip and continue to cook until second side is golden.
Remove cooked pancakes to a plate and tent with foil to keep warm (or keep in warm oven) and continue with remaining batter.