In a large mixing bowl, cream 1 cup butter and brown sugar until light and fluffy. Beat in eggs and 2 tsp. vanilla. Combine the oats, flour, 1 tsp. salt and baking soda; stir into creamed mixture. Press 2/3 of oat mixture into a greased 15” x 10” x 1” baking pan.
In a saucepan, combine the milk, chocolate chips and remaining butter and salt. Cook and stir over low heat until chocolate is melted. Remove from the heat; stir in walnuts and remaining vanilla. Spread over crust. Sprinkle with remaining 1/3 oat mixture.
Bake at 350° for 25 minutes or until golden brown. Cool on wire rack. Cut into squares.