Whisk together the flour, powdered sugar, and almond flour in a medium bowl.

Add cold butter chunks and flatten and rub the butter into the dry ingredients between your hands until it's a sandy texture.

Add the cold egg and mix with your hands or a fork until the dough comes together.

Dump the dough out onto the counter and knead with the palm of your hand for a few minutes, just until the dough is smooth.

If the dough is too warm, wrap it in plastic wrap and refrigerate it for 15-20 minutes.

Roll the dough out between two silicone mats (or parchment paper) until it's between 3mm to 5mm thick. Place the dough onto a baking sheet and into the freezer for 15 minutes (still in the silicone mats).

Line two baking sheets with perforated air mats and set aside. Alternatively, you can use parchment paper; however, you'll need to blind bake the tart shells.

Take the dough out of the freezer and use one of the tart rings to cut out 8 circles. These will be the bottoms of your tart shells. Use an offset spatula and slide it under the chilled dough to move the circles into the tart rings on the perforated mats. (If the dough becomes too warm to move without messing it up, place it back in the freezer for 5-10 minutes.

Cut 8 long strips out of the dough (you may need to reroll the dough and pop it back in the freezer from time to time to maintain the proper cold temperature). Carefully place these strips into each tart ring, pressing against the sides so it sticks.

Place the assembled tart shells in the freezer for 30 minutes. Preheat the oven to 160° C.

After removing from the freezer, trim the tops of each shell with a sharp paring knife.

Bake for 20 minutes and then carefully remove the rings and bake for another 5 minutes, or until golden brown. Let the shells cool on the perforated mat completely before filling.