Step 1: Prepare the Dough

1. In a large mixing bowl, cream together the softened butter, granulated sugar, and powdered sugar until light and fluffy.
2. Mix in the egg yolk and almond extract until well combined.
3. Gradually add the flour and salt, mixing until a soft dough forms.
4. Wrap the dough in plastic wrap and refrigerate for 30 minutes to firm up.

Step 2: Shape the Cookies

1. Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
2. Roll the chilled dough into a rectangle about 1/4-inch thick. Cut the dough into small triangles or crescent shapes to mimic the look of croissants.
3. Place the cookies on the prepared baking sheet.

Step 3: Add the Topping

1. Brush the tops of the cookies with the beaten egg white.
2. Sprinkle slivered almonds over each cookie and press them gently into the dough.
3. Lightly sprinkle granulated sugar on top for extra sweetness and crunch.

Step 4: Bake

1. Bake the cookies for 12-15 minutes, or until the edges are golden brown.
2. Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.

Step 5: Add the Optional Glaze

1. In a small bowl, mix the powdered sugar, milk or water, and almond extract until smooth.
2. Drizzle the glaze over the cooled cookies for an extra touch of sweetness.