Prepare Batter:
In a bowl, whisk together flour, baking powder, and salt. In another bowl, whisk milk, egg, and vanilla. Gradually add wet ingredients to dry, mixing until smooth.

Coat Marshmallows:
Dip each marshmallow into the batter, then roll in breadcrumbs or crushed graham crackers to coat completely.

Heat Oil:
Heat vegetable oil in a deep fryer or heavy-bottomed pot to 350°F (175°C).

Fry Marshmallows:
Carefully fry marshmallows in batches for 1–2 minutes or until golden and crispy. Remove with a slotted spoon and drain on paper towels.

Serve:
Dust with powdered sugar or drizzle with chocolate sauce if desired. Serve warm.