Cranberry Turtle Bars

Preheat oven to 350°F.

Line a 15- by 10-inch shallow pan with foil, leaving a 2-inch overhang on two short sides. Butter all four sides.

Blend flour, brown sugar, and salt in a food processor, then pulse in butter until mixture resembles small (roughly pea-size) crumbs. Sprinkle into baking 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.

Melt butter in a 3-quart heavy saucepan over moderate heat and stir in sugar, corn syrup, and salt. Boil, stirring over moderately high heat, occasionally, until caramel registers about 245°F on thermometer, about 8 minutes. Carefully stir in cranberries, then boil until caramel returns to 245°F. 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 6 crosswise strips, then cut into 6 lengthwise strips to form 36 bars.

Melt half of chocolate in top of a double boiler or a metal bowl set over a saucepan of barely simmering water, stirring until smooth. Remove bowl from heat and add remaining chocolate, stirring until smooth. Transfer chocolate to a small heavy-duty sealable plastic bag. Seal bag and snip off a tiny piece of one corner to form a small hole, then pipe chocolate decoratively over bars. Let stand at room temperature until chocolate sets, about 1 hour.