Preheat oven to 350°F. Grease a 13x9-inch baking pan and set aside.
In a large mixing bowl, cream butter, then add in flour, sugar, and salt until mixture is crumbly. Press 2 cups of the crumb mixture onto the bottom of the pan, reserving the rest. Bake for 10-12 minutes, or until edges are golden brown. Leave oven on.
In a small heavy-duty saucepan, combine 1 cup of chocolate chips and sweetened condensed milk. Over low heat, melt chocolate chips and blend into milk, stirring until smooth. Stir in vanilla extract, then spread evenly over the hot crust.
Stir the nuts and remaining chocolate chips into the reserved crumb mixture and sprinkle over the chocolate/milk mixture. Return pan to oven and bake for 25-30 minutes or just until set. Remove and allow to cool on a rack. Drizzle caramel topping evenly over top.