Preheat the oven to 350 degrees F. Spray a 9x9-inch or 11x7-inch pan with nonstick spray.
PREPARE THE CHOCOLATE LAYER:
Melt the chocolate chips, sweetened condensed milk, butter and salt in the top of a double boiler or carefully over low heat (or microwave in a glass bowl). Remove from heat and add the 1/2 cup walnuts and 1 teaspoon of vanilla. Set aside.
PREPARE THE CRUST:
In a medium bowl, sift together the flour, baking soda and salt. Set aside.
In a separate, large bowl, use an electric mixer to cream together the butter and brown sugar. Mix in the egg and 1 teaspoon vanilla. Stir in the sifted dry ingredients and the oats.
Press 2/3 of the mixture into the bottom of the prepared pan. Spread with the chocolate filling mixture. Crumble the remaining batter over the filling and sprinkle with the walnuts.
Bake for 25 to 30 minutes, or until lightly browned. Cool completely and then cut into small bars.
Notes
This recipe is one that my Mom used to make all the time when I was little. I'm sure she probably got the original recipe from a magazine or from one of the Pillsbury bake-off booklets.