Rhubarb-Blackberry Sauce

I am a sucker for recipes for Rhubarb ever since I had my first taste of Rhubarb pie, I've never been able to get away from my love affair with Rhubarb. This one is great because of the lack of sugar(unusual for rhubarb), the blackberries add a great flavor as well, who would have thought 2 of my favorite things would be good in anything together besides jam.

• 2 cups fresh or frozen rhubarb, cut into 1/2-inch pieces
• 2 cups fresh or frozen blackberries
• 2 tablespoons unsalted butter
• 1 pint vanilla ice cream, homemade or store-bought

In a small pot, combine rhubarb, 1 cup blackberries, and butter. Cover tightly, and cook over the lowest possible flame for 8 minutes, or until rhubarb is tender. Stir occasionally to prevent sticking. Add remaining blackberries and heat through. Pour over ice cream and serve.