Cut a slice out of a blood orange. Juice the remainder of the blood orange.
Place a sugar cube in an old-fashioned glass. Soak sugar cube with orange bitters.
Add blood orange juice and a splash of soda. Stir until sugar is entirely dissolved.
Add 2 oz. whisk(e)y.
Add ice.
Stir, add more soda if needed.
Garnish with reserved blood orange slice.