You can keep the rosemary simple syrup in the refrigerator for a week or so. You can do this ahead of time. Also, if blood oranges are hard for you to come by - navel oranges are also delicious.
Combine the water, sugar, rosemary, and bay in a small saucepan over medium heat. Bring to a simmer for 3-5 minutes, or long enough for the sugar to dissolve, stirring occasionally. Remove from the heat and let infuse for 10 minutes. Strain into a jar to cool completely.
In the meantime, juice and strain your oranges, you'll need 3 tablespoons / 1.5 ounces of juice for each drink.
To make each drink you're going to combine equal parts gin, juice, and tonic water with a bit of syrup and ice. So, its 3 tablespoons / 1 1/2 oz gin, 3 tablespoons / 1 1/2 oz freshly squeezed blood orange juice, and 1-2 teaspoons of the rosemary syrup in each tall glass (I used kolsch glasses here). Stir to combine, fill each glass 2/3 full with ice and top off with 3 tablespoons / 1 1/2 oz tonic water. Stir again and you're set.
