Preheat the oven to 350°F. Line 4 cups of a muffin tin with paper liners.

Pour the milk into a small bowl. Add the vinegar and let it sit while you prepare the rest of the ingredients.

Sift together the flour, cocoa powder, baking soda, and baking powder in a small bowl.

In another bowl, whisk together the canola oil, vanilla and brown sugar. Add the dry ingredients to the oil and brown sugar mixture in two batches, alternating with the milk mixture. Finally, stir in the graham cracker chunks.

Divide the batter between the 4 muffin cups and bake for 16-18 minutes, or until a toothpick inserted comes out clean.

Let cool completely before topping with marshmallow fluff and brûléeing with a kitchen torch to your desired level of doneness. For a lightly toasted marshmallow, hold the torch about 3″ from the fluff and keep it moving constantly. Leaving the flame in one place for too long will cause black spots! Be careful!

Serve immediately—they do not store well after the marshmallow fluff is toasted.