Use the wedge of grapefruit to rub the rims of 6 margarita glasses with grapefruit juice. Dip the rims in the kosher salt to coat. Set aside as you prepare the margaritas.
Place the tequila
, vodka, simple syrup, grapefruit juice, lime juice and ice in a bar blender
and puree until smooth. Divide the margarita
between 6 glasses and garnish
with the grapefruit quarters.