This is the best copycat version recipe I have tried besides the original. So try making this yourself with this recipe if you do not want to pony up the $$$. Let me know if you think it comes close to the original.
Copycat Momofuku Cornflake Marshmallow cookies
makes 20 cookies
2 sticks unsalted butter at room temperature
1 ¼ cup packed Organic dark brown sugar
1/3 cup granulated sugar
2 Organic eggs
2 tsp vanilla extract
1 3/4 cups all-purpose flour
1 tsp Aluminum Free baking soda
1/2 tsp baking powder
1 ½ tsp kosher salt (plus more for sprinkling)
3/4 cup Organic oatmeal
1 1/4 cup lightly crushed cornflakes (= about 1 1/2 cup cornflakes before crushing)
2/3 cup mini chocolate chips*
about 3/4 cup mini marshmallows
*the chocolate chips in the original Momofuku Milk bar cookie are minis, though substitute with regular-sized chips if you prefer
Preheat the oven to 350 degrees. In a mixing bowl, beat together the butter, brown sugar, and granulated sugar until light and fluffy, about 2-3 minutes on medium speed. Add the eggs and vanilla extract, and beat until combined.
Add the flour, baking soda, and salt and beat on low speed, just so the dry ingredients become incorporated. With a wooden spoon, mix in the oatmeal, crushed cornflakes, and chocolate chips.
(If you have time and would like the cookies to spread a little less, refrigerate the dough for two hours.)
On a parchment-lined baking sheet, scoop up and roll the dough into golf ball-sized spheres. (Six will fit comfortably on one pan–give them room to spread!) Lightly press down 4 mini marshmallows in the center of each ball of dough. Sprinkle tops with a touch more salt. Repeat with the remaining dough.
Bake for 9-10 minutes. The cookies will still look soft in the middle when you take them out of the oven. Allow them to cool directly on the tray for a few minutes before moving them onto a platter.