To make the thyme simple syrup, add all ingredients to a small saucepot. Bring to a boil over medium-high heat, stirring occasionally, until sugar is dissolved. Transfer to an air-tight container and cool to room temperature, then cover and refrigerate until chilled, at least one hour.

When you’re ready to make the margarita, add flaky sea salt and lime zest to a shallow bowl that’s slightly larger than your cocktail glass and mix with clean hands until well combined and fragrant. Rub a lime half around the edge of the glass, then dip into the salt mixture to coat to rim. Set aside while making the cocktail.

In a cocktail shaker, muddle blackberries and lime juice until berries have broken down and released their juices. (If you don’t have a muddler, the handle of a wooden spoon or rubber spatula will work, too!) Add thyme simple syrup, silver tequila, cointreau, and ice. Shake for 30-45 seconds, or until well chilled. Pour through a strainer into your prepared glass. Top with sparkling water and garnish with extra blackberries, and thyme sprigs, if desired. Serve immediately.

Note: the margarita ingredients make one cocktail, but the ingredients can easily be double or tripled in one shaker. The lime salt yields enough for about 4 cocktails, and the thyme simple syrup yields enough for about 16 cocktails. It keeps well in the refrigerator for up to 2 weeks.