Set your margarita glasses in the freezer for 10-20 minutes to get nice and cold before you prepare the margaritas.
Fill a shallow bowl or lipped plate with coarse salt. Run a lime wedge around the rim of the chilled glasses. Invert the glass into the salt to coat the rim.
Add ingredients to the blender: frozen peaches, peach juice, lime juice, simple syrup, tequila and ice.
Blend on high power until the margaritas are smooth, thick, and evenly combined.
Transfer the frozen margarita into glasses and serve immediately, garnished with lime wedges and/or peach slices.
Notes
For a sweet touch, rim the glasses with coarse sugar. For spice, use Tajin.
Frozen peach margaritas are best when served immediately from the blender. If you want margaritas on the rocks, you can double or triple the recipe and keep it chilled in the fridge. Don't add ice until you are ready to serve so the peach margaritas aren't watered down.
If fresh ripe peaches are available, use those. They have more flavor than frozen. To use fresh peaches: pit, peel, and slice them. Then place the peaches in the freezer in a single layer until frozen.