Combine the tamarind paste and water in a pot and bring to a boil, stirring with a whisk. Immediately turn off heat, cover, and let sit for 30 minutes on the counterl.
Stir and strain the mixture into a bowl, discarding any solids. Let cool to room temperature.
Make the Tamarind Margarita
Mix Tajin Seasoning with the salt and place on a small flat plate. Prepare two coupe glasses by running the edge of half a lime against the edges. Gently press the edges of the glasses into the salt mixture, and refrigerate the glasses.
Combine the tamarind syrup, Blanco tequila, simple syrup, lime juice, triple sec, and ice in a cocktail shaker.
Shake and pour into coupe glasses with salted rims. If using margarita glasses or tumblers, pour the entire contents of the shaker in the glasses and add ice if needed. Serve.
Notes
Make the tamarind syrup far enough ahead of time so that it has time to cool before you need it. Do not use tamarind concentrate directly in the cocktail, it will be too sour and strong.
You can use sea salt to rim the cocktail glass, but I highly recommend combining chili lime seasoning and salt. It takes it to the next level!
Try a quality orange liqueur such as Grand Marnier instead of triple sec.
To spice it up, muddle a few slices of jalapeno with the lime juice and simple syrup before adding the rest of the ingredients to the cocktail shaker.