In a shaker, add the ice then pour in the tequila or mezcal, cointreau, blood orange juice. Shake well.
Pour into a coupe or high ball glass.
Top the drink with Fresca or club soda and garnish with an orange slice.
Notes
Top the margarita off with a dusting of Tajín to the rim for an additional depth of flavor.
Use a jigger when measuring the alcohol and the other ingredients so that the drink is balanced.
Do not add the soda before shaking the ingredients as this will cause the drink to bubble and fizz and splatter everywhere. Wait until you combine the blood orange juices and the tequila, then top off with the soda.