Preheat oven to 350 degrees. Grease a 9-by-5-inch loaf pan and line with parchment paper so that a small amount overhangs the long ends like a sling.

Grate zest from all three oranges and place in a bowl with sugar. Using your fingers, rub ingredients together until orange zest is evenly distributed in sugar.

In small bowl, combine the blood orange juice, buttermilk or yogurt and vanilla bean paste. Whisk to combine. Pour mixture into bowl with sugar and whisk well. Whisk in eggs.

In another bowl, whisk together flour, baking powder, baking soda, salt and cardamom. Gently whisk dry ingredients into wet ones. Switch to a spatula and fold in olive oil a little at a time.

Scrape batter into pan and smooth top.

Bake cake for about 55-60 minutes, or until it is golden and a knife inserted into center comes out clean. Cool on a rack for 10 minutes, then use the overhanging parchment paper to pull the loaf out of the pan and place on a wire rack, allowing it to cool to room temperature.

For the glaze: In a small bowl, whisk together the powdered sugar and enough blood orange juice to get a thick but pourable glaze. Place the cooled loaf, still on the wire rack, over a sheet pan lined with parchment or foil. Pour the glaze evenly over loaf, allowing it to drip down the sides. Decorate with candied blood orange slices if desired.