The night before, pour the rosé into two ice cube trays (you might need three trays depending on the size, but two should do it!) and freeze.
When it’s time to make the frosé, place the ice cubes, rosé syrup, lemonade and lemon zest in a blender. Blend until it’s a slushy-like consistency. I like to refrain from adding ice until I see the consistency. Some rosé’s freeze different, so you might need a handful or 2 of ice to make it more slushy. If it’s TOO icy and won’t blend, add more of the rosé from the bottle that you used for the syrup!
Pour the froze into glasses and serve with a garnish of lemon.
Combine the wine and sugar in a saucepan over medium heat. Whisk until the sugar dissolves and the mixture starts to bubble, then turn off the heat. Let it cool completely. If you made it ahead of time (you totally can!), store it in the fridge until you're ready to use.