Grease an 9x9" square metal baking pan or line it with parchment paper. Preheat the oven to 350F.

In a large bowl mix together the flour, sugar and salt. Add the butter, egg and almond extract to the flour mixture. Mix well with your hands until the dough is smooth and completely incorporated. Press the dough into the prepared baking pan evenly.

Brush a thin layer of egg white on top of the dough and sprinkle with sliced almonds. Bake for 25 to 30 minutes until the edges and bottom are light golden brown. Remove from the oven, allow to cool to warm, then cut into squares in the baking pan. Allow the squares to cool to room temperature before removing from the baking pan.