Heat small saucepan over low heat. When pan is warm, add butter and let melt, swirling pan occasionally to coat bottom of pan with butter.
Once butter is melted, add Brown Swerve. Whisk well and cook 3 to 4 minutes, until sweetener has completely dissolved. Whisk often to prevent sweetener from sticking or burning.
Remove saucepan from heat. Add heavy cream to saucepan and stir to incorporate, then return saucepan to heat. Increase temperature under saucepan to medium-high.
Bring liquid to boil, then immediately reduce heat under saucepan to low. Cook 10 to 12 minutes, whisking frequently, until caramel sauce is thick enough to coat whisk or back of spoon without running or dripping off.
Serve caramel sauce immediately, or transfer caramel to glass jar with airtight lid and refrigerate until ready to serve. If refrigerating sauce, remove from refrigerator and bring to room temperature before serving, or slowly reheat in microwave or on stovetop over very low heat, stirring frequently to prevent separation.