While the brownies bake, make the pecan pie filling. Add butter, light brown sugar, maple syrup, heavy cream, cornstarch, salt and vanilla extract to a sauce pan. Bring the mixture to a boil over medium heat . Stir fairly frequently while the mixture heats up. Once the mixture begins to boil, reduce the temperature to low - medium heat. Simmer for about 2- 3 more minutes. Remove the sauce pan from the heat and stir in the pecans.
¼ cup (57 g), 4 tablespoons unsalted butter, sliced , ½ cup (100 g) light brown sugar, ½ cup (120 ml) maple syrup, 2 tablespoons (30 ml) heavy cream, 2 teaspoons (10 ml) vanilla extract , 1 teaspoon cornstarch, ½ teaspoons salt, 2 cups (190 g) pecans, roungly chopped