Preheat the oven to 400°F and line a baking sheet with parchment paper.

Use a fork to poke several holes in each sweet potato. Rub the skins evenly with oil and place them on the prepared baking sheet.

Bake for 1 hour, or until the sweet potatoes are very tender when pierced with a fork.

Carefully slice each sweet potato lengthwise. Gently mash the inside with a fork, keeping the skins intact. Add ½ tablespoon butter to each potato and mash slightly more until the butter melts.

Sprinkle chopped chocolate evenly over the mashed sweet potatoes, then top each with 2–3 marshmallows.

Switch the oven to broil and return the baking sheet to the oven for 30 seconds to 1 minute, watching closely, until the marshmallows are lightly toasted.

Remove from the oven and immediately sprinkle with crushed graham crackers.