In a large bowl, combine melted butter, oil, and brown sugar; beat until well mixed. Add eggs and whisk until pale and bubbly. Mix in vanilla and maple syrup.
Gradually add dry ingredients to wet, mixing until just combined. Fold in chocolate chips. Spread dough in prepared pan and top with extra chips if desired.
Bake for 25-35 minutes until edges are golden and a toothpick inserted comes out clean. Cool before slicing.
Notes
For best results, do not over-mix the batter to keep bars chewy and tender.