Step 1

Combine flour, oats, brown sugar, and salt in a medium bowl. Using your fingertips, rub in butter until moist crumbs form and no dry flour remains. Cover and chill. DO AHEAD: Can be made 1 day ahead. Keep chilled.

Step 2

Preheat oven to 350°. Coat a 13x9x2” baking dish with nonstick spray; set aside. Stir butter in a medium saucepan over medium heat, swirling occasionally, until melted, deep golden brown, and dark brown bits form at the bottom of pan (do not burn), 7–8 minutes. Pour into a medium bowl; let brown butter cool slightly.

Step 3

Whisk flour, oats, baking powder, cinnamon, and salt in a large bowl; set aside. Whisk brown sugar, eggs, and vanilla in another large bowl until mixture is smooth.

Step 4

Slowly stream brown butter into brown sugar mixture, whisking constantly; whisk until well blended. Add pears to dry ingredients; toss to coat. Stir into brown sugar mixture (batter will be thick). Using a spatula, scrape batter into prepared pan. Smooth top. Scatter chilled topping over batter.

Step 5

Bake blondie until golden brown, edges pull away from sides of pan, and a tester inserted into the center comes out almost clean, with a few moist crumbs attached, 30–35 minutes. Transfer to a wire rack and let blondie cool completely in pan.

Step 6

Cut blondie into squares. Dust with powdered sugar just before serving, if desired.