Feel free to swap walnuts or almonds for the pecans, or use half nuts and half dried cranberries for tart, chewy bars.
Preheat the oven to 350° and line the bottom of a 9-by-13-inch baking pan with parchment paper. Spread the pecans in a pie plate and toast for about 8 minutes, until golden. Chop the pecans and let cool.
In the bowl of a standing electric mixer, beat the butter and oil with the granulated sugar and brown sugar until creamy. Beat in the egg and vanilla until smooth. In a small bowl, whisk the flour with the baking soda and salt; beat the dry ingredients into the mixer at low speed. Add the chocolate chips and pecans; beat just until incorporated.
Transfer the dough to the prepared baking pan and press into an even layer. Bake for about 20 minutes, until lightly browned and nearly set in the center. Let cool completely, then run a knife around the edges and invert the rectangle. Peel off the paper and invert onto a cutting board. Cut and serve.