1) In a large saucepan, add the sugar, golden syrup, salt and melted butter. Stir to combine well. Add the eggs and 100g chopped pecans. Bring to the boil over medium heat.
2) Reduce the heat, and simmer stirring frequently for 10 minutes. Add the vanilla and remove from the heat to cool completely. Set aside.
3) Preheat the oven to 180C/Gas 4. Line a 20- by 20-cm baking tin with aluminium foil.
4) In a saucepan, over low heat, melt the butter and unsweetened chocolate, constantly stirring to incorporate. Set aside.
5) In a large bowl, add the sugar and the eggs. Using a hand-held mixer, beat together until well combined. Add the flour, vanilla, and the salt. Fold in the milk chocolate morsels.
6) Add the butter and chocolate mixture that had been set aside. Mix together with a spatula while folding in the remaining 100g 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 the trifle.
7) In a large bowl add the cream and the sugar and whisk together until soft peaks form.
8) To assemble, layer the brownies, pecan mixture, whipped cream, caramel syrup, and toasted whole pecans, as desired in a trifle dish.
Cook's Note: It is recommended that the trifle be chilled for 2 hours before serving.