Whisk together egg yolks and sugar in top of a double boiler with simmering water beneath. Whisk until smooth.
Add blood orange juice, zest, and salt to egg mixture and whisk until smooth. Heat over double boiler about 8-12 minutes or until thickened.
Remove curd from double boiler and add about 1 tablespoon of butter at a time, stirring after each addition, until melted and smooth.
Pour curd into container and place a piece of plastic wrap directly on top of curd. Refrigerate for up to 2 weeks.
SNAPPY TIPS: Substitute a little lemon or lime juice for the blood orange juice for a different taste.SNAPPY SUBSTITUTIONS: Fresh blood orange juice and zest are better, but omit the zest and use bottled juice if necessary.