Step 1

In a medium saucepan over medium heat, combine the orange juice, sugar, water, lemon juice, orange zest, and citric acid and let simmer for 10 minutes, stirring occasionally.

Step 2

Turn off the heat and let the zest infuse in the syrup for an hour.

Step 3

Strain the syrup with a fine mesh strainer into a lidded jar and refrigerate until chilled, about 3 hours and up to 1 month.

Step 4

When ready to serve, fill glasses with 1 part syrup to 2 or 3 parts seltzer (depending on your taste), then top each serving with a few scoops of vanilla ice cream. Serve immediately.