Preheat oven to 350 degrees. In mixing bowl, cream 1 cup butter and brown sugar. Beat in eggs and 2 tsp. vanilla. Separately combine oats, flour, 1 tsp. salt, and baking soda; stir into creamed mixture. Press two-thirds of oat mixture into greased 15x10-inch baking pan. In a saucepan, combine milk, chocolate chips, and remaining butter and salt. Cook and stir over low heat until chocolate is melted. Remove from heat; stir in walnuts and remaining vanilla. Spread over crust and sprinkle with remaining oat mixture. Bake in preheated oven for 25 minutes or until golden brown. Cut into squares. Makes 4 dozen.