Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking pan.
In a large bowl, beat together 1 cup butter and brown sugar until fluffy. Mix in eggs and 2 teaspoons vanilla. In another bowl, combine oats, flour, baking soda, and 1 teaspoon salt; stir into butter mixture. Set aside.
In a medium saucepan, heat sweetened condensed milk, chocolate chips, 2 tablespoons butter, and 1/2 teaspoon salt over low heat, stirring until smooth. Remove from heat. Stir in walnuts and 2 teaspoons vanilla.
Pat 2/3 of the oat mixture into the bottom of the prepared pan. Spread chocolate mixture evenly over the top, and dot with remaining oat mixture.
Bake for 30 to 35 minutes in preheated oven. Let cool on a wire rack, then cut into bars.