In a large saucepan over medium heat, combine the sweeteners and 4 tablespoons of the butter. Bring to a boil and cook 2 to 4 minutes, watching carefully so it doesn't burn. Remove from heat and add the cream. The mixture will bubble vigorously.

Sprinkle the surface with xanthan gum and whisk to combine. Whisk in the salt. Let the caramel cool until thickened but still pourable, 30 to 60 minutes.

Meanwhile, preheat the oven to 350ºF and line a cookie sheet with parchment or a silicone baking mat. Spread the pecans out on the mat in a single layer and bake 7 to 10 minutes, until toasted. Arrange the pecans in clusters of 3 or 4, making about 24 clusters. (If your pecans are large, use only 3 per cluster).

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.

Sprinkle with sea salt if desired, and let set.