Preheat oven to 350℉ and line cookie sheets with parchment paper.
In a large bowl, or stand mixer, cream butter with both sugars until smooth and creamy.
Add eggs, milk, and vanilla extract, stirring to combine.
Mix in flour, baking powder, baking soda, and salt until just combined.
Fold in graham cracker pieces and chocolate chips.
Scoop dough using small cookie scoop or a tablespoon onto prepared pans, spacing about 2 inches apart.
Bake for 12 minutes or until cookie edges are golden but centers are still slightly wet.
Remove from oven and place three marshmallows on top of cookies immediately, pressing gently.
Allow to cool on pan for 2 minutes before transferring to cooling rack.
Using torch, toast the marshmallows on cookies until toasted, careful not to set them on fire.