Sprinkle gelatin over 1 tablespoon water to bloom. Measure sweetener, salt and xanthan gum in a 4-6 cup capacity non-reactive metal pot. Add the eggs and yolks and whisk together until completely combined. Whisk in the buttermilk and heavy cream.
Place the pot over medium heat, whisking constantly until the mixture begins to thicken - about the 5 minute mark if using Tagatesse (or sugar) and 8 minutes for Sukrin :1 or Swerve. Turn the heat down to medium low and whisk vigorously for 1 minute. (The custard should bubble lazily if whisking stops.) Remove from heat and whisk for 1 1/2 minutes more. Tear the gelatin into pieces and drop into the custard, stirring until dissolved. Add vanilla and nutmeg, stirring to blend.
Let the mixture cool just slightly then pour into pre-baked pie crust. Level the top and arrange black berries, pushing them into the custard until they are at least 1/2 way submerged. Refrigerate uncovered for several hours before covering with cling film. Chill at least 6 hours before slicing and serving.
Sprinkle Tagatessse [Sukrin Melis, Swerve Confectioners (or powdered sugar if not low carb)] over the top and brown with a culinary torch. Pay particular attention to the black berries to make them look like they baked.
Serves 8. Each serving is 5 g NET CARBS. Nutritional information includes the crust specified and linked to.
**** I swapped out the low carb crust recipe shown in the photos because of its tendency to soak. The Low Carb Graham Cracker Crust resists soaking better. Nutritional information for the custard only: Calories: 181g, Fat: 15g, Carbs: 4.5g, Fiber: 1g, Protein 6g, NET CARBS: 3.5