Cream butter and sugar: In a large bowl, cream together the softened butter and granulated sugar until light and fluffy, about 2-3 minutes using an electric mixer.
Add almond flour and vanilla: Stir in the almond flour and vanilla extract.
Combine dry ingredients: In a separate bowl, whisk together the all-purpose flour and salt.
Combine wet and dry ingredients: Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Chill the dough: Cover the dough and refrigerate for at least 2 hours, or preferably overnight. This chilling period is crucial for preventing spreading and making the dough easier to handle.
Preheat and prepare: Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
Roll and cut: On a lightly floured surface, roll out the chilled dough to about ¼ inch thickness. Use heart-shaped cookie cutters (you'll need two sizes – one larger for the bottom and one smaller for the cutout in the top) to cut out the cookies. For half of the cookies, use the smaller cutter to cut out a heart shape in the center.
Bake: Place the cookies on the prepared baking sheets, leaving about 1 inch between cookies. Bake for 10-12 minutes, or until the edges are lightly golden brown. Be careful not to overbake.
Cool: Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.
Assemble the cookies: Once the cookies are completely cooled, spread about 1 teaspoon of Nutella on the flat side of each bottom cookie (the ones without the cutout). Top with a cut-out cookie.
Dust with powdered sugar (optional): Dust the assembled cookies with powdered sugar, if desired.