PREHEAT oven to 350° F. Grease baking sheet.
COMBINE flour, granulated sugar, baking powder and baking soda in large bowl; cut in butter with pastry blender or two knives until mixture resembles coarse crumbs.
COMBINE egg, milk and vanilla extract in small bowl; mix well. Add to flour mixture; stir with fork just until moistened. Form a ball with dough; divide dough in half. Cover; refrigerate for about 1 hour or until dough becomes easy to handle.
ROLL each half of dough on floured surface to 12 x 6-inch rectangle. Spread each rectangle with half of pastry filling to within 1-inch of edge. Top each filling with 1 cup morsels and half the nuts. Brush edges of each rectangle with water. Bring two long sides of each rectangle together over filling; seal seams and ends of each rectangle. Carefully transfer each rectangle, seam side down, with a pastry cloth or long metal spatula to prepared baking sheet about 3 inches apart.
BAKE 15 to 18 minutes until golden brown. Remove to wire racks to cool completely. Sprinkle with powdered sugar. Cut each loaf into eighteen 1/2 inch-thick slices.