Finely crush graham crackers using a food processor. Or, you’d like to get the kids involved, try putting the graham crackers into ziplock bags and letting them roll a rolling pin over them to crush them. Mix graham crackers crumbs, walnuts and chocolate chips by hand in a large mixing bowl. Add sweetened condensed milk, mixing by hand, until all of the dough is moist. Drop by teaspoonful onto a parchment paper-lined cookie sheet. The parchment is key—don’t try this recipe without it! If they flatten too much add more graham cracker crumbs to make a thicker dough. Cook 10-12 minutes until bottom of cookie is slightly brown. Cookie will still be very soft in the middle. Gently slide parchment and cookies off onto a wire rack. Flip parchment over and peel away from cookies. Parchment may be reused for the remainder of the dough.