In a large mixing bowl beat 1 cup butter on medium speed for 30 seconds. Add half the flour, all the brown sugar, eggs, 2 teaspoons vanilla and baking soda. Beat on low speed until throughly combined. Beat in remaining flour. Stir in oats.

In a medium saucepan cook chocolate chips, sweetened condensed milk, and 2 tablespoons butter over low heat until chocolate is melted, stirring occasionally. Remove from heat. Stir in remaining vanilla and nuts.

Pat 2/3 of the oat mixture into bottom of baking pan. Spread chocolate mixture over oat mixture. Dot with remaining oat mixture. Bake 25 minutes or until top is light golden. (chocolate mixture will still look moist.) Cool on wire rack and cut into bars.