1 Preheat oven to 325°F. Lightly coat an 8-inch round spring-form pan with cooking spray. Place a glass baking dish (any size) half-filled with water on the lower rack of your oven.
2 In a small bowl, combine plums, chocolate and water. Let stand 5 minutes until plums soften and chocolate melts. Stir.
3 In a food processor, combine plum mixture, flour, cocoa powder, brown sugar and salt. Whirl until nearly smooth.
4 In a large mixing bowl, use a hand whisk or mixer to beat eggs and granulated sugar until thick and foamy. Stir in half the plum mixture.
5 With a spatula, gently fold in remaining plum mixture and 1/2 cup chopped walnuts. Do not over mix. Pour into prepared pan.
6 Arrange walnut halves evenly around edge. Sprinkle remaining 1/4 cup chopped walnuts in center. Bake 25-30 minutes or until the center feels set when gently touched. Cool completely before slicing. Serve room temperature or chilled.

Source:

California Walnut Board