Preheat your oven to 175°C (350°F). Line a 9x9 inch (23x23 cm) square tin with parchment, leaving some overhang so you can lift the brownies out later.
Make the brownie layer: In a large bowl, whisk together the melted butter and chocolate chips until smooth. The warmth of the butter should melt the chocolate. Add both sugars and whisk until combined. Mix in the eggs and vanilla.
Sift in the flour, cocoa powder and salt, then fold everything together until just combined. Don’t overmix or your brownies will lose their fudgy texture.
Spread the batter evenly into the prepared tin and bake for 20 minutes. The brownies won’t be fully baked yet – that’s exactly what you want.
Make the pecan pie topping: While the brownies are in the oven, melt the butter in a saucepan over medium heat. Stir in the brown sugar, maple syrup and cream. Let it bubble gently for 1 to 2 minutes, then take off the heat. Stir in the vanilla, salt and pecans. Let it cool for a few minutes so it thickens slightly.
Take the brownies out after 20 minutes and carefully spoon the pecan topping over the top, spreading it evenly.
Return the tin to the oven for another 20 to 25 minutes, until the edges are set and the topping is bubbling and golden.
Let the brownies cool completely in the tin, then chill them before slicing into neat squares. Use the parchment overhang to lift them out easily.