Chill a champagne flute in the freezer for 5 minutes.
Pour 2 oz fresh blood orange juice into the glass.
Tilt the glass and add 4 oz chilled sparkling wine slowly down the side, watching the color swirl from pale to deep red as it mixes.
Stir once, gently, with a bar spoon.
Cut a thin wheel from a blood orange and set it on the rim.
Serve immediately, before the color settles and separates.
Good to Know
Blood oranges are at their best from roughly December through March, so buy a few extra and freeze squeezed juice in ice cube trays for the rest of winter.