1Preheat oven to 325F. In a medium saucepan, melt the butter with the cocoa over medium heat, stirring and removing from the heat as soon as the butter melts. Stir until smooth, then stir in the sugar. Stir in the eggs and vanilla until smooth, then add the flour and salt and stir just until combined.
2Pour into an 8x8-inch baking dish that has been buttered or sprayed with nonstick spray; smooth the top. Bake for 20 to 25 minutes, then let cool completely.
3To make the topping, stir together the brown sugar, syrup, butter, eggs and vanilla until smooth. Stir in the pecans and pour over the base. Bake for 35-40 minutes, or until golden and set.
4Let cool completely, then refrigerate for at least two hours before serving.