Preheat the oven to 350°F and set the oven rack to the middle position. Line an 8" x 8" baking pan with foil, so it hangs over all sides. Spray the foil with cooking spray.
To make the crust, in a food processor, combine the Almond flour, Swerve confectioners sweetener, and salt. Pulse about 5 times until it's well combined.
Scatter the 8 tablespoons of butter over the mixture. Pulse about 10 times until the mixture resembles wet sand.
Pour the mixture into the lined baking pan, and press it down well. Bake for about 20 minutes, or until the crust is golden brown.
While the crust is baking, combine the egg yolks, whole eggs, lemon zest, Swerve granulated sweetener, and sugar in a saucepan. Whisk well to combine.
Heat the mixture over medium-high heat, and add the 4 tablespoons of butter. Gently whisk until the mixture reaches 170°F. Be careful to not overcook it or the eggs will start to scramble!
Remove it from the heat, and add the cream. Set the mixture aside.
Remove the crust from the oven, and if there are any bubbles, gently tap them down. Let the crust sit for about 2 minutes, and with a spatula, gently tap it down to make sure it's set.
Very carefully, pour the warm lemon mixture evenly over the crust. Return it to the oven and bake for another 15 minutes, or until the lemon filling is set. When you shake it, it should wiggle only slightly.
Remove the pan from the oven, and let it cool on a baking rack for about 30 minutes.
Refrigerate the pan for at least an hour.
Cut into 16 bars, and if desired, sprinkle with powdered sugar, or Swerve confectioners sugar.
Refrigerate any leftover lemon bars in a covered container for 3-4 days