Preparation

1 Preheat oven to 325°F. Line a 9 x 13 x 1-inch pan with aluminum foil, pressing foil against sides and corners of pan with edges hanging over sides of pan.
2 In a large bowl, whisk together flour, corn starch, icing sugar, cocoa and salt.
3  Add softened butter and mix, using hands, until mixture is moist and crumbly. Press firmly over prepared pan. Bake for 30 minutes.
4 Combine butter, brown sugar, honey and salt in a 3-quart saucepan over medium heat. Bring to a boil and continue cooking for 3 minutes.
5 Remove from heat. Once bubbling stops, stir in heavy cream and rum extract. Stir in walnuts. Pour over shortbread base, spreading walnuts evenly. Pack firmly.
6 Turn down oven temperature to 300°F and continue baking for an additional 20 minutes. Remove carefully from oven (filling will be very loose, but will set as it cools).
7 Let stand at room temperature for at least 2 hours. Once completely cooled, use overhanging foil to lift out of pan.
8 Cut into squares or triangles and serve. Store in an airtight container, in the refrigerator, for up to one week.

Source: California Walnut Board