Line a 9 " quiche pan with pastry and trim off excess around edge of pan. Place a piece of buttered aluminum foil, buttered side down, over pastry, gently press into pastry shell. This will keep the sides of the shell from collapsing. Cover foil with a layer of dried peas or beans. Bake at 400ºF. for 10 minutes, remove foil and peas. Prick shell, and bake 3 to 5 additional minutes or until lightly browned. Cool. Combine mayonnaise, flour, eggs, and milk, mix thoroughly. Stir in crab meat, cheese, and onion. Spoon into quiche shell and bake at 350ºF. for 30 - 40 minutes or until firm in center.