Heat oven to 180°C/350°F/160°FF
Heat butter in microwave until it's just melted. Set aside while you prep the other ingredients.
Line 3 baking trays with baking paper. See notes
Sift the flour, bi carb soda, baking powder and salt together. Set aside
In the bowl of a stand mixer, combine the cooled melted butter and sugars until well blended
Add the egg, egg yolk and vanilla and beat until light and creamy, then continue to beat on medium-high for another 5 minutes.
Stop the mixer, add the flour mixture and beat until almost combined
Remove bowl from stand, add the 4 crushed Graham crackers and choc chips then combine with a spatula. DO NOT OVERMIX
Using a large ice-cream scoop, scoop out balls of cookie dough
Make an indent in the top of each ball. Fill indent with 6-8 mini marshmallows, then roll back into a ball
Toss each cookie ball into the extra crushed crackers, then place onto prepared baking sheet, leaving plenty of space to spread. I put 6 on each large cookie tray
Bake cookies for 12 minutes, until lightly golden. Remove from oven and transfer the cookies (still on the baking paper) to a bench. After 5 minutes, transfer to a cake rack to cool.
Cookies will last well for a few days, in an airtight container