In a large saucepan over medium heat, combine the sweeteners and 4 tablespoons of the butter. Bring to a boil and cook 3 to 5 minutes, watching carefully so it doesn't burn. Remove from heat and add the cream. The mixture will bubble vigorously.
Return the mixture to heat and bring back to a boil. Boil 3 minutes, watching carefully. Sprinkle the surface with xanthan gum and whisk to combine. Whisk in the salt. Let the caramel cool until thickened but still pourable, about 1 hour
Meanwhile, preheat the oven to 350F and line a cookie sheet with parchment or a silicone baking mat. Spread the pecans out on the mat in a single later and bake 7 to 10 minutes, until toasted. Arrange the pecans in clusters of 3 or 4, making about 20 to 24 clusters.
Drizzle a few teaspoons of caramel over each pecan cluster, making sure some caramel is touching each of the pecans. Place the cookie sheet in the freezer to set the caramel.
In a small bowl set over a bowl of barely simmering water, combine the chocolate and the remaining tablespoon of butter. Stir until melted and smooth, then drizzle over the chilled clusters.