Add the ice cubes to your blender, filling it about halfway to ensure a good slushie consistency.
Pour in the tequila, orange liqueur, and freshly squeezed lime juice over the ice.
If you like extra sweetness, add the simple syrup now to balance the tartness of the lime.
Blend everything on high speed until the mixture is thick, smooth, and resembles a slushie, about 30-45 seconds.
Stop the blender and check the texture; it should be icy yet creamy. If needed, add a few more ice cubes and blend briefly again.
Pour the frozen margarita slushie into chilled glasses and garnish with lime wedges or a salted rim if desired.