In a 4 cup measuring cup with a spout, combine lime juice, orange juice, tequila, and simple syrup. Stir to combine. Taste and adjust sweetness as needed.
Pour margarita liquid into the small cups, leaving about ¼” space at the top of the cup.
Slice limes into rounds - you can get about 3 large rounds from each lime - you want them to be large enough in diameter to fill most of the top of the cup.
Cut a tiny slice in the center of each lime round and insert a popsicle stick.
Place the popsicle stick and lime into each cup, adjusting the position of the lime on the stick so that it rests at the top of the margarita liquid and the popsicle stick stands upright.
Freeze for 8 hours or overnight.
Loosen the popsicle from the cup by warming the outside of the cup with your hand. This should only take a few seconds. Then gently pull the popsicle free! Sprinkle the top of the lime with salt and/or dip the bottom of the popsicle into a little bowl of salt.
Eat immediately!
Notes
Place the cups on a baking sheet before putting them in the freezer if you have the room. This makes it easier to serve and you don't have to worry about them tipping over before they set.
Roll the limes on the counter before juicing. It makes the process easier.
Plastic lined paper cups work best for these margarita popsicles; they loosen easier from the plastic.
Make sure you cut the lime slices thick enough to fill out that space at the top. You should be able to get about 3 slices from each lime.