For the butter: Combine pecans and brown sugar in a food processor and pulse until coarsely chopped. Add the bourbon, if using, vanilla, butter, vanilla seeds and salt and pulse again until smooth. Scrape into a large ramekin. Cover with plastic wrap and refrigerate for at least 1 hour and up to 24 hours. Let soften again before using.
For the banana bread: Preheat the oven to 350 degrees F and place an oven rack in the middle. Liberally spray the bottom and sides of a 9- by 5- by 3-inch light metal loaf pan with nonstick cooking spray. Set aside.
Mix together the flour, sugars, baking powder, cinnamon, baking soda and salt. Set aside. Mix together the butter, oil, vanilla, bananas and eggs in another bowl. Lightly fold the wet ingredients (banana mixture) into the dry ingredients using a rubber spatula until just combined. The batter should be thick and chunky (do not over-mix; the batter should not be smooth). If you over-mix, the bread will become rubbery!
Scrape the batter into the prepared pan. Bake until the bread is golden brown and a toothpick inserted into the center comes out with a few moist crumbs attached, 50 minutes to 1 hour. Let the bread cool in the pan on a wire rack for 15 minutes, and then remove the it from the pan. Serve slices warm slathered with the vanilla pecan butter.