Flour rolling surface and rolling pin lightly. Roll dough into circle. Trim 3 cm larger than upside-down 23 cm tart pan with removable sizes. Loosen dough carefully. Fold into quarters. Flour tart pan lightly. Unfold dough and press into tart pan. Trim edge even with top of rim. Prick bottom and sides thoroughly with fork 50 times to prevent shrinkage. Cover edge with double layer of foil to prevent over browning. Bake 10 to 15 minutes or until lightly browned. Cool to room temperature. To make cream cheese filling: Combine cream cheese, condensed milk, powdered sugar and lemon juice in small bowl. Beat at low speed of electric mixer until creamy. Place white chocolate chips and nuts in food processor work bowl. Process until finely chopped. Blend into cheese mixture. Spread in bottom of cooled baked tart shell. To make fruit filling: Combine blackberries, sugar, cornstarch and boysenberry syrup in medium saucepan. Cook and stir on medium heat until mixture is thickened and clear. Remove from heat. Stir in butter, lemon juice and salt. Transfer to bowl. Cool to room temperature. Spoon over cheese filling. To make topping: Sprinkle nuts over fruit filling in lattice fashion. To garnish: Combine powdered sugar, shortening, vanilla, butter flavoring and 3 tablespoons cream in medium bowl. Beat until smooth, adding more cream, if needed, for desired consistency. Spoon into decorator bag fitted with desired tip. Form decorative border around edge of tart. Refrigerate 1 to 2 hours. Remove rim. Cut into servings. Refrigerate leftovers. Notes: Use 23 cm pie plate if tart pan is unavailable. If tart is refrigerated longer than 2 hours, let stand at room temperature for a few minutes before serving. Makes 6 to 8 servings.