1. Preheat the oven to 350°F. Grease and flour an 8 x 8-inch pan.
2. Place the walnuts in the bowl fitted with the kneading/crushing blade. Mix at speed 12 for 50 seconds. Add all remaining ingredients and pulse 10 seconds to cut up butter. Launch the P3 pastry program.
3. Spread the mixture into the prepared pan. Bake for 35-40 minutes or until a knife inserted in the center comes out clean.
4. Cool for 1 hour before cutting.