Preheat the oven to 350°F. Spread the shredded coconut in an even layer on a baking sheet. Bake for 5–8 minutes, stirring once or twice, until lightly golden. Keep a close eye on it, as coconut browns quickly. Let cool completely.
Lightly spray a 9×13-inch pan with nonstick spray and set aside.
Place the butter in a large pot over medium heat.
Add 14 ounces of the mini marshmallows to the butter and stir until melted and smooth.
Stir in the vanilla and kosher salt.
Add the Rice Krispies cereal and toasted coconut, reserving a couple of tablespoons of coconut for topping. Stir until evenly coated.
Fold in the remaining 4 ounces of mini marshmallows.
Transfer the mixture to the prepared pan and lightly press into an even layer. Do not pack the mixture tightly.
Allow the treats to cool for 1 hour before cutting into 16 squares.