Spiced Oat and Pear Blondies

Name: Spiced Oat and Pear Blondies
Ingredients: ⅓ cup cup all-purpose flour; ⅓ cup cup old-fashioned oats; ¼ cup cup (packed) dark brown sugar; ¼ teaspoon tsp. kosher salt; 3 tablespoon Tbsp. chilled unsalted butter, cut into ½” pieces; Nonstick vegetable oil spray; ½ cup cup (1 stick) unsalted butter, cut into ½” pieces; 1½ cups cups all-purpose flour; 1 cup cup old-fashioned oats; 2 teaspoon tsp. baking powder; 1 teaspoon tsp. ground cinnamon; 1 teaspoon tsp. kosher salt; 1¾ cups cups (packed) light brown sugar; 2 large eggs; 1 teaspoon tsp. vanilla extract; 2 cups cups ¼” cubes cored peeled firm pears (such as Bosc or Bartlett; about 2 large); Powdered sugar (optional)