2 1/4 cups light brown sugar
2 cubes (8 ounces) unsalted, room temperature butter
14 ounces condensed milk
2/3 cup dark corn syrup
1/3 cup maple syrup
3 tablespoons molasses
1 1/2 teaspoons vanilla extract
1/4 teaspoon salt
Additional coarse salt for dusting
Combine the ingredients in a heavy saucepan over medium-low heat. Stir with a wooden spoon until the sugar dissolves (about 15 minutes), occasionally brushing down the sides of the pan to remove crystallized sugar. When fully dissolved, you can feel no crystals between your fingers in a bit of the cooled mixture.
Using a candy thermometer, increase the heat to medium-high and cook the caramel at a rolling boil until the temperature of the mixture reaches 236°F, stirring constantly, about 12 minutes. Pour the caramel into a metal bowl, but do not scrape the sides of the saucepan. Transfer the thermometer to the bowl and cool the caramel without stirring to 200°F with a clean wooden spatula, still brushing down the sides of the pan.
Line a 9 by 13 inch baking pan with parchment paper and pour in the caramel mixture to cool further. Sprinkle the top with about 3/4 teaspoon of kosher salt and place it in the refrigerator for 1-2 hours. Prepare wrappers for the caramel by cutting waxed paper into squares about 3 inches on a side. Slice the cold caramel into squares about 1 inch by 1/2 inch and wrap in the waxed paper, twisting the ends to close.