Preheat oven to 375ºF.

Whisk together flour, cocoa powder, baking soda and salt in a medium bowl, set aside.

Combine butter and sugar in a large mixer bowl and beat on medium speed until pale and fluffy, scraping down sides as needed. Add corn syrup, egg and vanilla. beat on medium speed for 2 minutes. Gradually add flour mixture alternately with milk until all is well blended.

Place graham cracker crumbs in a small bowl. Drop dough by rounded tablespoon into the bowl, and coat each dough ball with graham cracker crumbs. (Dough will be slightly sticky.)

Drop graham cracker coated dough balls onto a parchment lined baking sheet. Bake 6 to 8 minutes until set. Remove from oven and immediately press a marshmallow half on top of each cookie. Return to oven and bake an additional two minutes. Cool completely on a wire rack.

Once cooled, carefully "toast" the marshmallow of each cookie with a culinary kitchen torch. (An alternative method would be to place the cookies directly under an over broiler for about 30-60 seconds).