In a large bowl, whisk together flour, crushed cereal pieces, sugar, baking powder, and salt.
In a separate medium bowl, whisk together milk, melted butter, egg, and vanilla.
Pour wet ingredients into the dry ingredients, stirring until they’re just combined, but being careful not to over-mix. Some lumps are OK. Fold in Lucky Charms marshmallows.
Heat a griddle or frying pan over medium-low heat and lightly brush with butter or cooking oil. Pour about ⅓ cup batter onto the griddle and cook pancakes for about 2 minutes on each side, until they’re nicely browned. Repeat with all batter.
Serve pancakes with marshmallow fluff topping if desired. I like to melt the fluff in the microwave for about 15 seconds.