Preheat oven to 350º F. Lightly coat a 9 x 13 inch baking dish with butter and set aside. Additionally, you may line the 9 x 13-inch baking dish with parchment paper, leaving enough at the edges to easily lift the bars from the baking dish. Butter the parchment paper.
Whisk together the flour, sugar, baking powder, baking soda, and salt. Add in one egg, the melted butter, and the vanilla extract. Beat until well combined. Press the mixture into the bottom of the prepared baking dish. Sprinkle the chopped pecans on top of the cake mixture. Set aside.
Beat together the cream cheese, powdered sugar, and the two remaining eggs with an electric mixer until creamy and smooth. Pour on top of cake crust layer in the baking dish.
Bake until the top is golden brown, about 45 minutes. Cool before cutting and serving. If using parchment paper lined baking dish, allow to cool in the baking dish for about 5 minutes. Then, carefully lift the edges of the parchment paper and transfer the Park Avenue Bars to a wire rack to cool completely. Then, cut for serving.