First, chop the pecans and toast on the stovetop or in the oven. Set aside and allow to cool.

Preheat oven to 350°F. Line a 9x13-inch baking pan with foil, leaving a two-inch overhang on all sides. Butter or spray the sides (but not the bottom) of the foil with baking spray.

To make the base, blend flour, brown sugar, and salt in a food processor, then add butter and pulse until mixture forms pea-sized lumps. Pour into prepared pan, then press down firmly all over with a metal spatula to form an even layer.

Bake in middle of oven until golden and firm to the touch, 15 to 17 minutes, then cool in pan on a rack.

While base is cooling, melt butter in a 3-quart heavy saucepan over moderate heat and stir in sugar, corn syrup, and salt. Boil over moderately high heat, stirring occasionally, until caramel registers 245 degrees Farenheit on a candy thermometer, about eight minutes.

Carefully stir in cranberries. At this point the caramel will seize. Allow the caramel to melt back down, stirring, as necessary, to prevent burning. Boil until caramel returns to 245 degrees Farenheit.

Remove from heat and stir in vanilla, then stir in pecans until well coated.

Working quickly, spread caramel topping over base, using a fork to distribute nuts and berries evenly. Cool completely.

Lift bars in foil from pan and transfer to a cutting board. Cut into six vertical strips, then five horizontal strips to form 30 bars.

Melt chocolate in top of a double boiler, stirring until smooth. Alternately, melt in the microwave, stopping to stir every 20 seconds.

Transfer chocolate to piping bag or small heavy-duty sealable plastic bag. If using a sealable plastic bag, seal top and snip off a tiny piece of one corner to form a hole. Pipe chocolate decoratively over bars. Let stand at room temperature until chocolate sets, about one hour.