In a small, heavy-bottomed saucepan, melt the butter over medium-low heat. Stir in the heavy whipping cream, allulose, and erythritol-based sweetener. Over medium or medium-low heat, bring the mixture to 310 degrees F, stirring frequently to prevent burning. Once it reaches 310 degrees, immediately remove it from the heat. Stir in the pure vanilla and pecans. Set aside to slightly cool, then place in the fridge for 5 to 10 minutes to thicken. Line a baking sheet with parchment paper and drop Tablespoon-sized amounts of the caramel pecan mixture onto the parchment paper. Prepare the chocolate coating as directed below. Drizzle the chocolate over the caramel pecans, roughly 1 to 2 teaspoons per cluster. Place in the freezer for 30 minutes to an hour, or until set. Store in the fridge for up to 1 month or in the freezer for up to 3 months.
Chocolate Coating:
Place the chocolate chips and butter in a microwaveable-safe bowl. Heat for 45 seconds then stir. Heat for 20 seconds, then stir again. Repeat heating in 20-second intervals until melted.