Method:
Put raspberries, blackberries, blueberries, 1/2 cup of the sugar, salt and 1/4 cup water into a 4-quart pot and bring to a boil over medium-high heat. Reduce heat to medium-low.
Put 2 tablespoons of the remaining sugar, cinnamon, baking powder and flours into a bowl and stir well to combine; set aside. Put butter and milk into a small pot and heat over medium heat just until butter is melted and milk is warm, about 2 minutes. Add to flour mixture and stir just until combined to form a batter.
Drop batter by the spoonful over simmering berries to form 6 large dollops. Sprinkle with remaining 1 tablespoon sugar and nutmeg then cover and cook over medium heat until biscuits are cooked through and fruit is bubbling, about 15 minutes. Scoop onto plates and serve.