In a large saucepan, add 2 cups sugar, corn syrup, salt and 2/3 cup melted butter. Stir to combine well. Add the eggs and 1 cup chopped pecans. Bring to a boil over medium heat. Reduce the heat, and simmer stirring frequently for 10 minutes. Add 1 teaspoon vanilla and remove from the heat to cool completely. Set aside.
Preheat the oven to 350 degrees F. Line a 9 by 9-inch baking pan with aluminum foil.
In a saucepan, over low heat, melt 3 sticks butter and unsweetened chocolate, constantly stirring to incorporate. Set aside.
In a large bowl, add 2 1/2 cups sugar and the eggs. Using a hand-held mixer, beat together until well combined. Add the flour, 1 teaspoon vanilla, and the pinch salt. Fold in the milk chocolate morsels.
Add the butter and chocolate mixture that was set aside. Mix together with a spatula while folding in 1 cup of whole toasted pecans. Pour into the prepared pan and bake until the brownies are done, about 35 minutes Remove from the oven and allow to cool completely before assembling.
In a large bowl add the cream and 3/4 cup sugar and whisk together until soft peaks form.
In a trifle dish, layer the brownies, pecan mixture, whipped cream, caramel syrup, and toasted whole pecans, as desired.
Cook's Note: It is recommended that the trifle be chilled for 2 hours before serving.