Here's an easy and awesome recipe of his. And as David says, if you can't find Blood Oranges you can use tangerine, grapefruit or plain old orange juice. Just be sure it's fresh for the best taste.
Blood Orange Sorbet
1. Juice your blood oranges. The measure the juice.
2. For each 1 cup (250ml) of juice, figure 1/4 cup (50g) of granulated sugar to be added.
For example: Use 1/2 cup (100g) sugar for 2 cups juice (500ml).
3. Put the sugar in a small, non-reactive saucepan. Add just enough juice to saturate it very well. Heat, stirring frequently, until the sugar is completely dissolved.
4. Stir the sugar back into the reserved blood orange juice.
5. Chill thoroughly, then freeze in your ice cream maker.