Combine melted butter, oil, and both sugars in a bowl, then beat in eggs and optional vanilla extract.
Gradually mix in flour, cocoa powder, and salt until just incorporated.
Pour batter into a greased (or lined with foil or parchment paper) 9x13 inch baking dish.
Bake in a preheated oven at 350°F until the top begins to set and slightly jiggles, about 15 minutes. Remove from oven.
In a saucepan, stir together brown sugar, maple syrup, melted butter, beaten eggs, optional vanilla, and chopped pecans. Simmer over medium heat, stirring until the mixture thickens, approximately 5 minutes.
Pour this pecan mixture over the partially baked brownie layer in the pan.
Return to the oven and bake at 350°F until the pecan layer is set but still a bit jiggly, about 20 minutes. Allow to cool before enjoying!