Preheat oven to 325F and line a baking sheet with parchment paper.
In a food processor or high powered blender, grind macadamia nuts until they resemble coarse meal and clump together (a few larger bits are okay).
Transfer to a bowl and whisk in almond flour, sweetener, baking powder, xanthan gum and salt. Stir in butter, egg and lime zest until dough comes together.
Turn dough out onto prepared baking sheet and pat into a low, long log about 4 x 10 inches. Bake 20 to 25 minutes, until edges are just golden brown and top is firm to the touch. Remove from oven and let cool completely.
Reduce oven temperature to 250F. With a VERY sharp, non-serrated knife, cut into 12 slices (a straight up and down motion works better than sawing back and forth).
Place slices cut-side down on the same parchment-lined baking sheet and bake 15 minutes, then gently flip and bake another 10 to 15 minutes. Remove and let cool completely.
For the glaze, whisk together sweetener and lime juice in a small bowl. Drizzle over cooled biscotti.
Notes
Serves 12. Each serving has 4.05 g of carbs and 2.09 g of fiber. Total NET CARBS = 1.96 g.Food energy: 162kcal Saturated fatty acids: 3.06g Total fat: 15.51g Calories from fat: 139 Cholesterol: 5mg Carbohydrate: 4.05g Total dietary fiber: 2.09g Protein: 3.32g Sodium: 97mg