Start by lining a 9×13-inch baking dish with parchment paper, allowing it to overhang on the sides. Lightly spray the parchment with nonstick cooking spray to prevent sticking.

In the bowl of a stand mixer, pour in 1 cup of ice-cold water. Sprinkle the gelatin evenly over the water and whisk gently. Let it sit for 5 minutes to properly hydrate.

In a large heavy-bottomed saucepan, combine the remaining cold water, sugar, and corn syrup. Cook over medium-high heat, stirring until the sugar dissolves before letting it boil until it reaches 252°F.

Once it reaches 252°F, remove the pan from heat and allow the syrup to cool down to 212°F.

With the mixer on low speed, carefully pour the hot syrup into the bloomed gelatin. Mix on low for about 30 seconds, then increase to high and beat for 11–13 minutes until the mixture turns thick and glossy.

Now, add the vanilla extract and give it another quick mix for about 10 seconds to fully incorporate the flavor.

Lightly spray a spatula with nonstick cooking spray, then pour the marshmallow mixture into the prepared pan. Use the spatula to smooth the top, creating an even layer.

Drizzle the warmed caramel sauce over the marshmallow mixture. Use a toothpick or a knife to create large swirls, taking care not to overmix.

Generously sprinkle flaky salt over the top, adding that delightful contrast to the sweetness.

Let your marshmallows sit uncovered at room temperature for at least 4 hours, or overnight, until they are fully set and firm.

In a small bowl, combine the confectioners' sugar with cornstarch. This will help coat the marshmallows and keep them from sticking.

Dust a pizza cutter with the sugar-cornstarch mixture before cutting the set marshmallows into squares. Dredge each cut side in the mixture for an extra fluffy coating.

Place your marshmallows in an airtight container and store at room temperature for up to 3-5 days; they'll remain soft and delicious!