Prepare the Cookie Dough:

1. Cream Butter and Sugar:
   • In a large mixing bowl, beat the softened butter and sugar with an electric mixer on medium speed until light and fluffy (about 2–3 minutes).
2. Add the Egg and Extracts:
   • Beat in the egg, vanilla extract, and almond extract (if using) until well combined.
3. Combine Dry Ingredients:
   • In a separate bowl, whisk together the all-purpose flour, almond flour, and salt.
4. Mix the Dough:
   • Gradually add the dry ingredients to the wet ingredients, mixing on low speed until the dough comes together.
5. Chill the Dough:
   • Divide the dough in half, flatten each half into a disk, wrap in plastic wrap, and refrigerate for at least 1 hour (or up to 24 hours).

Roll and Cut the Cookies:

6. Preheat Oven:
   • Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper or silicone mats.
7. Roll Out the Dough:
   • On a lightly floured surface, roll out one dough disk to about 1/8-inch (3 mm) thickness. Keep the other disk in the refrigerator until ready to use.
8. Cut the Cookies:
   • Use a heart-shaped cookie cutter to cut out as many cookies as possible. For half of the cookies, use a smaller heart-shaped cutter to cut out the center, creating a “window.”
9. Transfer to Baking Sheets:
   • Place the cookies on the prepared baking sheets, spacing them about 1 inch apart.

Bake the Cookies:

10. Bake:
    • Bake for 8–10 minutes, or until the edges are lightly golden. Rotate the baking sheets halfway through baking for even cooking.
11. Cool:
    • Let the cookies cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.

Assemble the Cookies:

12. Spread the Nutella:
    • Spread about 1 teaspoon of Nutella on the flat side of each solid cookie.
13. Top with the “Window” Cookie:
    • Gently press a cookie with a cut-out center on top of each Nutella-covered cookie to create a sandwich.
14. Dust with Powdered Sugar:
    • Sprinkle the tops of the cookies with powdered sugar for a beautiful finish.