Preheat the oven to 400 degrees.  It is quickest to mix the crisp in the food processor: put the flour, the sugars, cinnamon and salt in the work bowl fitted with the metal blade. Process briefly to blend the dry ingredients. Drop in the butter pieces and pulse a dozen or so times, until the butter has been uniformly cut into a sandy powder of small bits. Sprinkle on the water and process for a couple of seconds only, just to moisten the dough; it should still be rather loose and granular.
To mix by hand, blend the dry ingredients in a large mixing bowl and cut in the butter to the grainy powder with a pastry cutter. Toss the powder and water with a fork to moisten.

Line the baking sheet with the parchment paper. Sprinkle the loose grains of dough evenly—in one layer—in an oval shape about 8-inches by 12-inches, filling in any holes and keeping the layer thin: don’t compress them. Bake for about 10 minutes, and then rotate back to front, for even heating. The crumbs will have melted together, spread out in a thin layer and perhaps started to bubble. Bake for another 7 to 10 minutes or more, until the layer is deeply caramelized, golden brown all over (and probably very dark on the edges). It will resemble a giant brown sugar cookie.

Set the pan on a wire rack and cool until the cookie is very crisp. Cut or break off any burnt edges. Crack the cookie into crispy flakes, an inch or smaller. This is a good size for munching; you can crumble them up a bit more when layering the parfait.