Preheat the oven to 350 degrees F.
Combine the butter and 1 cup of sugar in a large bowl, and beat with a hand mixer until light and fluffy. Beat in the egg yolk and almond extract.
Add the flour and salt and beat until the dough comes together.
Press the dough into an even layer in the bottom of a quarter sheet pan. For a thinner, flakier cookie, use a half sheet, but don't press the dough all the way to the edges. There's no need to grease the baking sheet, the dough has enough butter to prevent sticking.
Beat the egg white with your hand mixer (make sure to wash the beater!) until it is light and fluffy, but not to the point of stiff peaks.
Using an off-set spatula, spread the beaten egg white out on top of the cookie dough.
Sprinkle the almond slices evenly over the egg white-painted dough.
Finally, mix the remaining tablespoon of sugar with the cinnamon and sprinkle it evenly over the top of the cookie dough.
Bake the cookies for 30-35 minutes (shorter if you're going the thinner cookie route).
As soon as you take the cookies out of the oven, slice them into diamond shapes, by making overlapping diagonal cuts.
Let the cookies cool completely before you remove them from the pan. Break them into diamond shapes and store in an airtight container.