PREHEAT oven to 375° F. Grease 13x9-inch baking pan.
BEAT butter and brown sugar in small mixer bowl; beat in 1-3/4 cups flour. Press onto bottom of prepared baking pan.
BAKE for 12 to 15 minutes or until lightly browned. Cool completely in pan on wire rack.
SPREAD jam over crust. Combine walnuts and sugar in small bowl; set aside 2 tablespoons for topping. Beat eggs until light in large mixer bowl; beat in remaining walnut mixture, 2 tablespoons flour and vanilla extract. Stir in 1 cup morsels. Pour over crust.
BAKE for 20 to 25 minutes or until top is set. Immediately sprinkle remaining morsels over top. Let stand for 5 minutes until morsels are shiny; spread. Sprinkle with reserved walnut mixture. Cool; refrigerate for 10 minutes to set chocolate.
Makes about 4-1/2 dozen 1-inch bars.