Preheat the oven to 350 degrees.

Line a 15 x10 x 1inch baking sheet with heavy duty foil.

In a large mixing bowl, beat one cup of butter until light and fluffy. Add to this half the flour. Then add the brown sugar, eggs, 2 teaspoons of vanilla extract and the baking soda. Beat this until it's well combined, scraping down the sides of the bowl as needed. After this is well mixed, add in the remaining flour and stir well. Add in the oats and stir well again. This dough will be very stiff. Set the mixture aside.

In a small saucepan, heat the chocolate chips, the can of sweetened condensed milk, and 2 tablespoons of salted butter over low heat, stirring often. Heat just until all the chocolate is melted, then remove from heat and stir in 2 teaspoons vanilla extract.

Take about 3 1/2 cups of the dough and press it evenly into the bottom of the foil lined baking sheet. Then pour the chocolate filling over the top, and spread it evenly almost to each edge. Drop the remaining dough by teaspoonfuls over the top of the chocolate layer.

Bake at 350 degrees for about 25 minutes or until the dough on top is lightly browned. (The chocolate layer will still look a little moist.) Cool in the pan on a wire rack. Remove from the pan, by gently pulling up the foil edges. Cut into bars and store in the fridge.