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.