Rim the glass with salt or sugar by running a lime wedge around the edge and dipping it on a small plate.
Add tequila, limoncello, lime juice, simple syrup, and ice into the blender.
Blend on high until the ice gets smooth and the mix looks slushy.
Taste and adjust sweetness or tartness if needed.
Pour into the prepared glass and garnish with a lemon or lime wedge.
Notes
Fresh lime juice and crushed ice improve flavor and texture. Add soda for lightness or more limoncello for strength. Great for doubling, but blend in batches.