Preheat oven to 400F. Line a 12-cup muffin tin with paper liners. In a large bowl, combine flour, 3/4 cup sugar, baking powder, baking soda and salt. Stir in partridgeberries. In another large bowl, beat together egg, orange juice, oil and orange zest. Add to dry ingredients all at once. Stir just to moisten. Spoon evenly into muffin cups, filling 3/4 full. Sprinkle tops with a pinch of sugar. Bake 15-20 minutes, or until a toothpick inserted in centre of muffin comes out clean. Makes 12 muffins.