For the crust

1. Preheat the oven to 375°F. Line an 8×8-inch pan with parchment paper and grease with butter or non-stick cooking spray. Set aside.
2. In a bowl, mix melted butter (or browned, if desired), sugar, and vanilla. Add flour, oats, and salt and stir until incorporated. Reserve 1/2 cup of dough for topping. Transfer remaining dough to the prepared pan, and press the dough evenly across the bottom of the pan. Bake for about 18 minutes or until golden. Transfer crust to rack and let cool while you prepare the filling. Keep oven on.

For the filling

1. In a small heavy saucepan over medium heat, melt butter until deep nutty brown, stirring often and watching carefully, about four to six minutes. Be careful not to burn! Immediately pour browned butter into glass measuring cup to cool slightly.
2. In a separate bowl, whisk together sugar, eggs, vanilla, and salt. Add flour, cinnamon, and nutmeg and whisk until smooth. Gradually whisk browned butter into sugar-egg mixture; whisk until well blended. Fold in the chopped pears.
3. Carefully pour browned butter mixture onto the cooled crust. Sprinkle with reserved crumble topping. Bake bars until golden, and a tester inserted into center comes out clean, about 35-40 minutes. Cool bars completely in pan on rack.
4. Use the parchment paper to remove cooled bars from pan and cut into squares with a very sharp knife. Store at room temperature in a covered container.