Zest the oranges as finely as you can
Add water and sugar to a saucepan. Bring to a simmer as you stir until the sugar has dissolved, and the liquid reduced by about half.
When the sugar is fully dissolved, remove from the heat, and stir in the chopped mint leaves and orange zest.
Let the liquid sit for about 20 minutes at room temperature.
While the syrup steeps, juice the oranges, discarding any seeds you find. Strain out any pulp.
You should have about 3 cups of juice.
Stir in the Cointreau.
When the syrup has steeped for 20 minutes, and the orange juice is ready, strain the syrup, and add to the orange juice.
Pour the liquid into a baking dish or roasting pan large enough so that the liquid is about 1-inch deep, or less.
Put it into the freezer for about 1 hour.
Remove from the freezer, and use two forks to scrape and break up the ice.
Return the dish to the freezer, and let it freeze solid. It should take about 2 to 3 hours. Scrape with the forks to break it up every 30 to 45 minutes.
When it’s fully frozen, it’s best served immediately, garnishing with the remaining fresh mint. You can also cover with plastic wrap and keep in the freezer.,