Roll medium-sized lemons on the counter for 30 seconds to soften and maximize juice yield.

Cut lemons in half and juice using a citrus juicer or by hand, then strain through a fine mesh sieve to remove pulp and seeds.

If making homemade simple syrup, combine equal parts sugar and water in a saucepan over medium heat, stir until sugar dissolves (about 2 minutes), then cool before using.

Pour fresh lemon juice, simple syrup, and cold water into the blender to create an even liquid base.

Add ice to the blender, filling it about three-quarters full to achieve the desired slushy texture.

Add a pinch of sea salt to enhance the tartness and round out the flavors.

Pulse on low speed a few times, then blend on high for 30 to 45 seconds until the mixture is smooth and slushy.

Pour the lemon shake up into tall glasses and serve immediately with straws.