Melt the butter in a skillet over medium heat, then stir in the sweetener and heavy cream.
Lower the heat and let it simmer for 20–30 minutes, whisking often, until it thickens enough to coat a spoon and leaves a clean line when you drag your finger across it.
Add the white chocolate chips, pumpkin puree, maple syrup, and pumpkin pie spice, whisking until the chocolate melts and everything is smooth.
Turn off the heat, stir in the vanilla, then pour the mixture into an 8x8 dish lined with parchment paper.
Freeze for at least 2 hours (or overnight) before slicing and serving.
Notes
Nutrition per serving: Calories: 357, Total Carbs: 4g, Net Carbs: 4g, Fats: 33g, Protein: 2g