Shortbread crust:

1. Cream the butter and granulated sugar on medium until light and fluffy (2-3 minutes). 
2. With the mixer on low, add the egg, salt and vanilla extract, mixing until just combined.
3. Add the flour and beat on low-medium until the dough forms a cohesive ball and pulls away from the sides.
4. Wrap in plastic wrap and refrigerate for at least 30 minutes.

Filling:

1. In a food processor, pulse the almonds and powdered sugar until mixed and the almonds have been reduced to a fine crumb.
2. Whip the egg whites on high until soft peaks form.
3. Fold the egg whites into the almond/powdered sugar mixture, folding gently so the egg whites don't deflate. Mix until just combined.

Assembly:

1. Line the bottom of a 9" springform pan with a piece of parchment.
2. Remove the shortbread dough from the refrigerator and set aside 1/3 of it (about 175g).
3. Roll the remaining dough out on a lightly floured surface until you have an 11" circle.
4. Gently transfer the dough to the parchment paper lined pan, and press it into the bottom and about 1" up the sides.
5. Pour the filling into the crust, spreading it evenly to the edges.
6. Use a small pairing knife to trim away any excess crust more than 1/4" above the filling. 
7. Roll the remaining dough out on a lightly floured surface until you have a 9 1/2" circle.
8. Cut the dough into 1" wide strips and arrange on top of the filling in a latticework pattern.
9. Trim the excess dough from around the edges.
10. In a small bowl, whisk the egg yolk and brush over the latticework pieces of crust.
11. Bake at 350F for 40-45 minutes, or until the crust is golden brown and the filling is set (there will be a gentle jiggle but there shouldn't be sloshing).
12. Remove from the oven and allow to cool completely before removing from its pan.