Collect the zest from one grapefruit. Cut four two-inch long strips of the zest from the second grapefruit, and slice them thinly. Collect three tablespoons of juice from either or both of the grapefruits.

Use non stick cooking spray to coat two six-cavity donut pans.

Preheat oven to 350 degrees.

In a large bowl, combine flour, 1 1/2 cups sugar, baking powder, ginger, and salt, and mix well.

In a small bowl, combine buttermilk, egg, canola oil, vanilla, and the zest of one grapefruit, and whisk until combined.

Add the wet ingredients to the dry and stir.

Spoon batter into pans, filling each cavity to a bit over 3/4 full.

Bake for 25-30 minutes. Allow to cool in pan for five minutes before turning donuts out on a wire rack to cool completely.

In a small bowl, whisk powdered sugar and grapefruit juice until smooth, then set aside.

In a small saucepan, combine strips of zest, 3 tablespoons sugar, and 3 tablespoons water, and bring to a boil.

Reduce heat to a low flame, and simmer until sugar has dissolved. Strain.

Toss zest immediately in remaining unused sugar until coated.

Transfer to cutting board and chop.

Dip the top of each donut carefully in the glaze, then place on a wire rack glaze side up, allowing the excess to drip off. Sprinkle immediately with chopped zest.