Fill a glass 3/4 of the way with ice and add the freshly squeezed blood orange juice.
Add gin and a splash of simple syrup. Don't use a heavy hand on the syrup unless you want the drink to be sweeter! A little goes a long way.
Top off with lime seltzer and a sliced blood orange.
I used 12oz glasses–definitely adjust the proportions if you're using a larger glass!