Pre-heat oven to 325 F and grease two 11x17-inch baking sheets. Beat together butter, sugar and egg yolk with an electric mixer until light and fluffy. Stir in flour and cinnamon. With your hands, pat dough into a very thin layer over one baking sheet and half of the second. This can be time-consuming to get an evenly thin layer, but it doesn't have to be perfect. Aim for 1/4-inch thickness (this may take up more than half of the second pan). For flakier, more delicate cookies, make them thinner....for less flaky but less delicate cookies, make them thicker (you may have to bake them a couple minutes longer if they are thicker). Beat egg white and water in a small bowl until frothy. Spread over dough. Arrange the almonds in a mosaic pattern on top. Bake for 15 to 20 minutes or until golden brown. Remove from oven and slice into rectangle or diamond shapes while hot.