Add sugar to a cocktail shaker. Squeeze the juice from the limes into the shaker, then add in the limes.
Using a muddler or back end of a wooden spoon, crush the limes and sugar to release more juices, then give it a quick stir.
Add ice to the shaker and top with the vodka. Close it off with the lid and give it a few shakes.
Pour everything into a cocktail glass and garnish with a lime slice.
Enjoy!
Notes
You can use granulated or raw sugar. If using the raw/turbinado sugar, I recommend grinding it in a mortar and pestle first. Using white sugar will result in a clearer beverage, while raw sugar will add a hint of tan.
Another way to make this is to muddle the limes and sugar directly in a cocktail glass, then top with ice (cubes or crushed) and vodka. Stir, garnish with a slice of lime, and serve.