Place the rack in the multicooker and press Bake. Adjust the temperature to 350°Fand the timer to 2 hours, and let heat.
Coat an 8 1/2 × 4 1/2-inch loaf pan with cooking spray. Line the loaf pan with parchment paper, leaving 2 inches of overhang on both long sides. Spray the parchment.
In a medium bowl, whisk together the flour, baking powder, and salt.
In a large bowl, add the butter, brown sugar, and granulated sugar, and beat on medium-high with an electric mixer until light and fluffy, about 3 minutes.
Beat in the egg and vanilla extract. Reduce the speed to low and gradually add the dry ingredients, mixing just until incorporated. Fold in the chocolate chips and walnuts.
Spread the batter in the prepared loaf pan and place the pan on top of the rack. Cover with the lid and bake until a toothpick inserted into the center comes out clean, 1 hour 15 minutes to 1 hour 25 minutes. Press Cancel.
Remove the loaf pan, place it on a wire cooling rack, and let the blondies cool completely in the pan.
Using the overhangs, transfer the blondies to a cutting board and cut into 8 to 10 pieces.