In a large mixer bowl, cream together the butter and brown sugar
Beat in eggs and vanilla
Sift together flour, soda, and salt
Stir in oats
Stir dry ingredients into creamed mixture until blended, set aside
In heavy saucepan over low heat melt together sweetened condensed milk, chocolate pieces, remaining butter, and salt, stirring until smooth
Stir in nuts and remaining vanilla
Put 2/3 of oat mixture in bottom of 15 1/2x10 1/2x1" pan
Spread chocolate mixture over dough
Dot with the remaining oat mixture
Bake in 350° oven 25-30 minutes
Cool
Cut into 2x1" bars