For marshmallows. Spray an 11 x 15 cookie sheet with cooking spray and cover with parchment. Spray parchment with cooking spray and dust heavily with 1/4 cup confectioners sugar.
Combine 1/2 cup water with 3 packets of unflavored gelatin in electric mixer. Mix together using whisk attachment.
In a small saucepan, combine sugar, syrup, salt and remaining 1/2 cup water and cook over medium heat using a candy thermometer, to 240 degrees.
Turning on mixer to low speed, immediately pour in hot syrup, continue beating over high speed until marshmallow cools and thickens. This will take 10 to 15 minutes.
Immediately pour marshmallow on to prepared cookie sheet, using lightly sprayed spatula so marshmallow doesn't stick. Spread evenly and sprinkle top with remaining confectioners sugar. Allow to cool completely. Cut into about 80 squares with bench scraper, knife, or spatula If they are still too sticky, use more confectioners sugar on bench scraper.
For graham crackers, cream butter, vanilla and sugars in mixer.
Combine dry ingredients and add alternately with milk until all is combined.
Flatten dough into a rectangle, wrap in plastic wrap and chill for at least 1/2 hour.
Roll dough on floured surface with floured rolling pin, to about 1/8 inch thick.
Cut into 1-1/2 inch squares. You should have about 80 cookies.
Place on cookie sheets. You can place them pretty close together, since they don't spread. Prick with fork to prevent puffing.
Bake at 350 degrees for 12-14 minutes, until lightly browned.
While cookies are still hot, place one marshmallow on each. They should stick to cookie. Allow to cool before dipping.
Melt chocolate on 1/2 power in microwave or over double boiler.
Dip each cookie, one at a time in melted chocolate, marshmallow side down. Then turn over and lift out with a fork. Tap on bowl to allow excess chocolate to drip, scrape bottom of fork and place cookie on parchment, pushing off fork with another fork or knife. Touch up any open spots with chocolate. Allow to cool until chocolate is firm. Can be refrigerated to chill.