Melt butter in a large frying pan over medium heat. Stir in blackberries, blueberries, 1/4 cup sugar, and 1 tbsp. lemon juice. Cook until juices are released from fruit, about 4 minutes. Stir in thyme, then raspberries. Add more sugar and lemon juice to taste, depending on sweetness of berries. Serve warm over ice cream.
Note: Nutritional analysis is per 1/2-cup serving.