Combine 1 cup water and 1 cup sugar in a small saucepan over medium heat. Stir constantly until the sugar dissolves completely, about 3-4 minutes. You'll see the mixture get clear and shiny. Remove from heat and let this simple syrup cool for 10 minutes — don't skip this part or you'll scramble your melon.
Pour the cooled syrup into your blender with 4 cups cantaloupe chunks, 2 tablespoons lemon juice, and 1 tablespoon honey. Add 1 tablespoon orange juice for brightness and 1 teaspoon lemon zest. Blend on high until you get a completely smooth puree with zero lumps. This takes about 2-3 minutes in my Vitamix, but honestly any blender works fine.
Strain the mixture through a fine mesh sieve into a large bowl, pressing gently with the back of a spoon. This removes any stringy bits from the cantaloupe and gives you silky-smooth sorbet. I usually get about 4 cups of liquid here, which is perfect.
Whisk in 1 teaspoon agar-agar powder, 1/2 teaspoon ground cardamom, 1/4 teaspoon salt, and 1 teaspoon corn syrup directly into the strained mixture. Mix really well for about 1 minute until the agar-agar dissolves completely — lumps will ruin your texture. Taste it now and adjust sweetness or lemon if needed.
Pour the mixture into a 9x13-inch freezer-safe container, cover it with plastic wrap, and pop it in the freezer. Set a timer for 2 hours. After 2 hours, take a fork and scrape the edges and bottom really well, breaking up any ice crystals forming.
Stir the scraped mixture really well, breaking up bigger chunks with your fork. Return it to the freezer uncovered for another 2 hours. I scrape again at the halfway point (after 1 hour) if I remember — it makes a huge difference in texture.
After the final 2 hours, your cantaloupe sorbet easy should be frozen but still scoopable, almost like soft-serve. If it's too hard, let it sit at room temperature for 5 minutes before scooping. Scoop into bowls and serve immediately for that perfect creamy texture, then store the rest covered.