Prepare the Hazelnut Flour Mixture: In a medium bowl, whisk together the hazelnut flour and powdered sugar until well combined.

Whisk the Egg Whites: In a large, clean mixing bowl, beat the egg whites with an electric mixer until soft peaks form. Add the cream of tartar and continue beating.

Gradually Add Granulated Sugar: Gradually add the granulated sugar, about a tablespoon at a time, while continuing to beat the egg whites. Beat until stiff, glossy peaks form.

Fold Dry Ingredients into Meringue: Gently fold the hazelnut flour mixture into the meringue in two additions.

Prepare Baking Sheets: Preheat your oven to 300°F (150°C). Line two baking sheets with parchment paper.

Pipe or Spread the Meringue: Transfer the meringue mixture to a piping bag and pipe three even circles, about 8 inches in diameter, onto the prepared baking sheets. Alternatively, spread the meringue into circles using a spatula.

Bake the Meringue Layers: Bake for 60-75 minutes, or until the meringue layers are dry and lightly golden.

Cool the Meringue Layers: Turn off the oven and let the meringue layers cool completely inside the oven with the door slightly ajar.

Make the Cream Filling: While the meringue layers are cooling, prepare the cream filling. In a large bowl, beat the heavy cream with an electric mixer until soft peaks form. Add the powdered sugar and vanilla extract, and continue beating until stiff peaks form.

Assemble the Hazelnut Dacquoise: Once the meringue layers are completely cool, gently peel them off the parchment paper. Place one meringue layer on a serving plate. Spread half of the cream filling evenly over the layer.

Add Second Layer: Place the second meringue layer on top of the cream filling. Spread the remaining cream filling evenly over this layer.

Top with the Final Layer: Place the final meringue layer on top of the cream filling.

Chill the Assembled Dacquoise: Refrigerate the assembled Hazelnut Dacquoise for at least 30 minutes before serving.