Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper. Arrange the graham crackers in a single layer, covering the surface edge-to-edge. It’s okay to break a few to fit snugly—just try not to leave gaps.

In a medium saucepan over medium heat, melt the butter and brown sugar. Stir occasionally as it begins to bubble, then let it simmer for 2–3 minutes. You'll know it's ready when the mixture thickens slightly and smells like rich caramel. Turn off the heat and stir in the vanilla extract (step back—it will sizzle!).

Pour the hot toffee evenly over the graham crackers. Use a spatula to gently spread it so every piece gets a coat. Bake for 10 minutes, until the caramel bubbles and starts to darken.

Remove from the oven and immediately sprinkle chocolate chips on top. Return to the oven for 1–2 minutes—just long enough for the chocolate to melt.

Once out of the oven, use a spatula to spread the melted chocolate into a smooth layer. Sprinkle mini marshmallows on top. Let it cool at room temperature until completely set (about 1 hour), or refrigerate for 20–30 minutes if you're short on time.

Once firm, peel off the parchment and break into pieces. Uneven shards are part of the charm!