Preheat the oven to 400℉ and line a baking sheet with parchment paper.
Remove the sheet of puff pastry from the freezer; let it thaw just a bit on the counter while you mix up the almond filling.
1 sheet puff pastry
In a mixing bowl, combine the softened butter, sugar, almond flour, egg yolk, and almond extract.
1/4 cup butter, 1/3 cup sugar, 1/2 cup almond flour, 1 egg yolk, 1/4 teaspoon almond extract
Spoon the mixture into a resealable baggie and seal the baggie; set aside.
Place the puff pastry on a clean surface and open to a square.
Cut the square into 9 even squares and transfer them to the prepared baking sheet.
Using a small sharp knife, score (make a shallow cut) a square into each of the puff pastry squares about 1 centimeter smaller than the outer edges of the square (see photos above) to create a border.
Cut one corner off the baggie of filling and squeeze the filling into the inner squares of the puff pastry.
Whisk together the egg white and water; brush onto the outside borders of the puff pastry.
1 egg white, 1 teaspoon water
Sprinkle the pastries with sliced almonds.
1/4 cup sliced almonds
Bake for 12-15 minutes or until golden brown and puffy.
Dust with powdered sugar.
powdered sugar
Serve warm or at room temperature .