Preheat oven to 350 degrees.
Coat an 8 x 8 baking pan with cooking spray.
Melt butter and stir in macadamia nuts and Swerve.
Press into the bottom of the pan.
Bake for 20 to 25 minutes, until golden brown. Cool.
Whisk together eggs, egg yolks, and ½ cup Swerve in a bowl.
Add lemon juice, lemon zest, xanthan gum, and remaining ¼ cup of swerve to a sauce pan. Bring to a boil over medium high heat, whisking constantly. Cook for one minute.
Reduce heat to medium.
Take ¼ cup of the hot lemon juice and whisk it into the egg mixture.
Gradually add the remaining lemon mixture to the eggs and whisk until smooth.
Pour back into the sauce pan and cook for 5 minutes, whisking constantly, until the sauce is thickened.
Remove from heat and whisk in the butter, a spoonful at a time.
Allow to cool slightly. Transfer the mixture to a food processor or blender and process for 2 to 3 minutes, until fluffy and smooth.
Spread over the cooled crust.
Cover and chill for 4 hours.