Combine the tequila, Blue Curacao and lime juice in a cocktail shaker, or in a covered mason jar. Then shake, shake, shake everything together.
Pour sugar syrup into a shallow bowl; spread the black seas salt in a separate shallow bowl - make sure both dishes are wide enough for the rim of your margarita glass to fit into. Dip the rims first in the sugar syrup and then in the black salt, turning to coat the entire rim.
Carefully add 2-3 ice cubes to each glass without disturbing the salted rims.
Pour the margarita mixture carefully over the ice. Serve the drinks immediately.
If you're like me and don't own any margarita glasses (who has the space to stash all those cocktail-specific bar glasses??) my go-to is always the pint-sized mason jars! I have a ton of them on hand and they're perfect for a small drink.
Consider stashing your margarita glasses in the freezer ahead of time to get them really cold for your drinks.
The recipe below makes two modest-sized margaritas. If you're making drinks for more people or just second and third servings for yourself, you can double or triple the quantities listed.