Combine flour, dry milk powder, baking powder, sugar, and salt in a large mixing bowl; cut in shortening until mixture resembles coarse crumbs. Make a well in the center; add water all at once. Stir just until dough clings together.
On a lightly floured surface, knead dough gently for 10 to 12 strokes. Roll or pat dough to 1/2-inch thickness. Cut with a 2 1/2-inch biscuit cutter, dipping cutter into flour between cuts and rerolling dough scraps. Or pat dough into a 6x4-inch rectangle and cut dough into 2-inch squares.
Prepare a covered grill for indirect grilling. Test for medium heat where skillet will be placed. Lightly grease a large cast-iron skillet. Place biscuits 1/2 inch apart in skillet. Place skillet on grill. Cover and grill for 10 to 12 minutes or until bottoms of biscuits are golden and inside of biscuit is done.
Cool slightly. Split biscuits and serve warm with jelly, jam, or marmalade.