Preheat oven to 350°F (180°C). Spray a 13x9-inch baking pan with baking spray with flour. Line pan with parchment paper, letting excess extend over sides of pan.

In a large bowl, whisk together brown sugar and ¾ cup (170 grams) melted butter until light and fluffy, 2 to 3 minutes. Whisk in 1 egg (50 grams) and egg yolk until smooth. Whisk in 1 tablespoon (13 grams) vanilla.

In a medium bowl, whisk together flour, pecans, baking powder, and salt. Using a rubber spatula, fold flour mixture into sugar mixture. Pour batter into prepared pan, smoothing top with an offset spatula.

In another large bowl, whisk together cream cheese, remaining ½ cup (113 grams) melted butter, remaining 2 eggs (100 grams), and remaining 1 teaspoon (4 grams) vanilla until well combined. Add confectioners’ sugar, beating until smooth. Spread onto crust mixture.

Bake until edges are golden brown and center jiggles slightly, 25 to 30 minutes. Let cool completely in pan on a wire rack.

Using excess parchment as handles, remove from pan, and cut into bars. Serve with Butter Pecan Sauce. Refrigerate in an airtight container for up to 3 days.