In a food processor fitted with a metal blade, combine the flour baking soda and salt, blending well. Add the shortening all at once and process until the mixture becomes coarse meal. Add the onion, celery seed, and red pepper flakes. Drizzle the water through the feed tube a little at a time, using only as much water as necessary for the batter to form a ball (the amount of water will vary with every batch). Divide the dough in half and on a well-floured board, roll out each half to 1/8-inch thickness. Cut into squares or rectangles with a knife or pizza cutter. Place the crackers on a lightly greased cookie sheet, piercing each cracker 3 times with a fork. Repeat for the remaining half of the dough. Bake at 350 degrees F. for 20 to 25 minutes or until medium brown. Cool on a wire rack.

Makes 50 to 60 crackers or enough for about 2 cups of dip.