Heat oven to 350 F. Cream 1 cup butter and brown sugar; blend in eggs, 1 teaspoon vanilla and salt. Combine flour, soda and oats; stir into creamed mixture. Spread two-thirds of the dough in a greased 9x13 baking ban. In a heavy saucepan, combine 2 tablespoons butter, milk and chocolate chips; cook over low heat, stirring constantly until butter and chocolate melt. Stir in 1 teaspoon vanilla. Spread chocolate mixture over dough in pan. Drop remaining dough by teaspoonfuls on top of chocolate layer. Bake about 25 minutes. Cool and cut into bars to serve.