Preheat the oven to 350°F (175°C). Use the middle rack so your marshmallows toast evenly without burning too quickly.

Break chocolate bars into smaller pieces and layer them evenly in the bottom of an oven-safe baking dish (an 8x8-inch pan or pie dish works great).

Cover the chocolate completely with marshmallows. You can use regular or mini marshmallows—just make sure they’re in an even layer.

Place the dish in the oven and bake for 5–10 minutes, keeping a close eye after the 5-minute mark. It’s done when the chocolate is melted and the marshmallows are puffed and golden brown.

Remove from the oven and let it sit for 1–2 minutes before digging in. Serve immediately with graham crackers or your favorite dippers.