Preheat oven to 350°F and set oven rack to the middle position. Lightly butter a 10"x15" baking tray, set aside.
Cream together butter and granulated sugar. Divide the egg and add the egg yolk, cinnamon, salt and almond extract. Beat to fully combine. Add flour and mix only until dough starts to come together.
Press or roll dough evenly into prepared pan. Whisk egg white with 1 tbsp water. Brush evenly onto prepared dough. Sprinkle evenly with almonds and then sprinkle with coarse sugar. Just enough to create a nice sparkle.
Bake for 20-22 minutes until lightly golden. Remove from oven and allow to cool on a wire rack for 3-5 minutes and then cut into squares or diamonds while the cookie is warm and soft. Once cut, allow to cool completely before removing from the pan. The cookies will firm up as they cool.
-coarse sugar is a larger crystal sugar that doesn't melt when baked so it keeps a sparkle on the goods it's sprinkled on. It may also be called pearl sugar, decorators sugar, sparkling sugar.
-I get about 45 - 2" diamond shaped cookies, plus the best and crispiest half diamonds around the edges.
-I've tried sliced almonds with and without the skin and both are good to use and is a matter of preference.
-I find it just as easy to cut the squares instead of just scoring them while they are warm, but if you're having difficulty just score them and cut when cool.
-cookies are best if eaten while fresh, however they will last in a sealed container at room temperature for several days. If freezing, allow to cool completely and store in an airtight container away from strong odours.