It was several years ago so I can't recall exact proportions but I juiced the blood oranges, used the Campari to taste (maybe a 1/2 ounce added in increments and taste) pulverized the fennel in a grinder (1 tsp perhaps and don't add all of it at once) and probably 4 oz. of white wine which needs to be reduced first. Once the sauce is done, and it's fast after the wine is reduced, monte the hard butter off the heat. You could zest the blood orange before cutting it and add the zest at the last minute as well as a squeeze of lemon if necessary.
You could consider using a tiny touch of saffron instead of the fennel.