Melt the 2 tbls. of butter in a small saucepan over moderate heat. Add the sweet red pepper, onion, and garlic; saute until the vegetables are soft, about 5 minutes. Add the rosemary and black pepper. Remove from the heat and allow to cool to room temperature.
In a medium bowl, blend the red pepper mixture with the 1/2 cup butter using a wooden spoon. Transfer to a sheet of heavy duty aluminum foil; roll the foil around the mixture, forming a log 8" long by 3/4" in diameter. Tuck in the ends of the foil, label, and freeze. Will keep for up to 2 months at 0*F. Use to flavor rice and vegetables or to spread on bread or rolls. A 1/4" slice equals 1 teaspoon.