Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine graham cracker crumbs, sugar, baking powder, and salt. Mix well to ensure even distribution of the dry ingredients.
Pour in the melted butter and milk. Stir until just combined, being careful not to overmix. The batter will be slightly lumpy, which is perfectly fine.
Grease a 9x13-inch baking dish and pour the batter into the dish, spreading it out evenly.
Sprinkle the chocolate chips evenly over the batter, then add the mini marshmallows on top.
If using, sprinkle the chopped nuts over the marshmallows for added crunch.
Bake in the preheated oven for 30-35 minutes, or until the edges are golden brown and a toothpick inserted in the center comes out mostly clean.
Remove the cobbler from the oven and let it cool for a few minutes before serving. For an extra touch, you can broil it for 1-2 minutes to achieve a toasted marshmallow effect on top.