Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.

In a bowl, combine melted butter, graham cracker crumbs, sugar, and salt. Press mixture into the baking pan.

In another bowl, whisk together pumpkin puree, condensed milk, pumpkin pie spice, vanilla extract, and egg until smooth. Pour mixture over crust.

Sprinkle chocolate chips over the pumpkin layer and press them in slightly.

Bake for about 15 minutes, or until edges are set and chips start melting.

Scatter mini marshmallows on top and return to the oven for another 10-15 minutes until golden brown.

Let cool completely, then cut into squares and serve.