Preheat oven to 350 F°. Line a large baking pan with a silicone baking mat or parchment paper and set aside.
In a medium size mixing bowl, cream the butter and sugar using a hand or stand mixer.
Add the egg and vanilla extract, continue mixing until just combined.
Add the dry ingredients into the bowl with the wet, using the mixer, mix until combined and dough comes mostly together.
Add the chocolate and using a wooden spoon mix this into the dough.
Scoop the dough using a cookie scoop, or into approximately 2 tablespoon amounts. Gently roll dough into a ball and place on the cookie sheet, giving 3 inches of space in between (should be able to easily fit 8-9 cookies on a sheet.)
Bake the cookies for 8 minutes, then carefully remove from the oven, place 2-3 mini marshmallows on top of each cookie, gently pressing down so they stick to the top of the cookie.
Place the cookie sheet back in the oven and continue baking an additional 2 minutes.
Remove and let the cookies cool on the baking sheet for 5 minutes then remove to a wire rack to continue cooling.
Continue until all cookie dough has been baked. Recipe makes 24 cookies.