1. Preheat oven to 350°. Spray a 10½-inch square cast-iron skillet with baking spray with flour. Set aside. 

2. In a medium bowl, beat cream cheese and butter until smooth and creamy, approximately 3 minutes. Add brown sugar, and beat until creamy. Add eggs, one at a time, beating well after each addition.

3. In a small bowl, combine bananas, sour cream, and extract, whisking to combine. Add banana mixture to butter mixture, beating to combine.

4. In a separate medium bowl, whisk together flour, baking powder, baking soda, and salt. Gradually add flour mixture to butter mixture. In a small bowl, combine walnuts and sugar. Spread batter into prepared pan. Sprinkle nut mixture over batter.

5. Bake until a wooden pick inserted near the center comes out clean, 25 to 30 minutes. Let cool in pan on a wire rack for 10 minutes before serving.