Preheat your oven to 350°F (175°C). Prepare a 8x8 or 9x9 inch baking pan by greasing it and lining it with parchment paper.

In a mixing bowl, cream together 1 cup softened butter, ¾ cup superfine white sugar and ¼ teaspoon salt until light and fluffy. Add 1 tablespoon pure vanilla extract and mix until fully incorporated.

Scrape the sides of the bowl and gradually add 2½ cups all-purpose flour to the butter mixture, mixing until just combined to avoid overworking the dough. The dough will be crumbly but hold together when pressed into a ball.

Press about two-thirds of the dough into the prepared pan, reserving the remaining dough for the top layer. Place the pan in the preheated oven and bake for about 15-17 minutes, until it's very lightly golden and no longer shiny on top.

To a medium bowl add ½ cup softened butter, ¼ teaspoon almond extract, 2 teaspoons pure vanilla extract, and 1 cup sugar. Mix with an electric mixer until creamy. Add 2 room temperature eggs and mix again until well combined.

To the butter mixture add 2 cups almond flour, 1 tablespoon all-purpose flour and mix again until fully combined into a creamy paste.

In a separate bowl crumble up the remaining ⅓ shortbread dough reserved earlier into small and medium-large pieces. Add 1 tablespoon brown sugar, ½ cup sliced almonds, ½ cup chopped pecans, and ½ cup chopped walnuts. Mix with a spoon until all ingredients are evenly distributed and the texture has become a crumble.

Pour the almond frangipane on top of the par baked crust and spread into an even layer. Use a spoon to evenly sprinkle the nutty crumble mixture on top of the frangipane.

Place your pan in the pre-heated oven and bake at 350F for 40 minutes or until the crumble on top looks golden brown, and the crumble in the middle no longer looks raw. Remove the pan from the oven and allow the bars to rest at room temperature for at least 30 minutes to cool and set.

Dust with 2 tablespoons powdered sugar cut into 18 triangles or 9 squares, serve and enjoy!