Preheat the oven to 350 degrees and set the rack to the middle position. Lightly grease a 9-inch springform pan.
In a food processor, combine the butter, almond flour, powdered sugar, salt, vanilla extract, lemon extract and lemon zest. Pulse about 20 times or until the mixture is combined and looks like damp sand.
Press the dough into the bottom of the springform pan. Prick the dough all over with a fork to let any steam escape while it bakes.
Bake the shortbread for 15-20 minutes or until it starts to turn golden brown.
Remove the crust from the oven and let it cool for about 15 minutes. Then, place it in the refrigerator for another 10-15 minutes to chill. When you place the crust in the refrigerator, take one container of sorbet out of the freezer and let it stand at room temperature for 10-15 minutes to soften.
When the crust is chilled and the sorbet is softened enough to scoop and spread easily, scoop it onto the crust and gently spread it over the entire crust. Place it in the freezer for 15 minutes to harden. While it's in the freezer, take the next container of sorbet out of the freezer and let it soften.
When the second container of sorbet has softened, remove the cake from the freezer and spread the second layer over the first. Place it in the freezer, and remove the last container of sorbet to soften.
Spread the last container of sorbet over the cake when it's softened, and return the cake to the freezer for about 2 hours to harden.
Before removing the cake from the pan, run a sharp knife around the entire inside edge of the pan to make sure the sorbet doesn't stick. Unlatch the pan and gently life the sides of the pan away.
If desired, garnish the cake with fresh fruit.