In a heavy skillet (I use cast iron), melt butter over low heat. When butter is completely melted, add onions. Adjust the heat to medium-low. Allow the onions to cook in the butter for 10 minutes, stirring once. Add the Brown Sugar Sweetener Substitute and salt. Allow onions to cook over medium/low heat another 10 minutes or until lightly browned. Serve as a topping for burgers or sandwiches. 8 servings