Prepare the grill for direct cooking over medium heat (180° to 230°C).
Prepare the grill for cooking over medium heat (200°C).
In a food processor puree the blackberries with the water. Add up to 2 tablespoons of sugar to taste.
In a small saucepan over medium heat on the stove, melt the butter, then add the remaining 1 tablespoon sugar and stir to dissolve. Remove the saucepan from the heat. Brush the peach halves all over with the butter mixture.
Brush the cooking grates clean. Grill the peach halves over direct medium heat, with the lid closed, until browned in spots and warm throughout, 8 to 10 minutes, turning every 3 minutes or so. Remove the peaches from the grill and serve warm with the blackberry sauce and frozen yogurt, if desired.
Brush the cooking grates clean. Grill the peach halves over medium heat, with the lid closed, until browned in spots and warm throughout, 8 to 10 minutes, turning every 3 minutes or so. Remove the peaches from the grill and serve warm with the blackberry sauce and frozen yogurt, if desired.