In a mixer, cream butter and sugars. Add the eggs.
Add the flour, baking soda, and oats slowly to the mixture. Spread ¾ of the oat dough into a sprayed 9x13 rectangular baking pan, spreading it evenly in the bottom. Bake bottom crust 12 minutes while preparing fudge sauce.
In a pot on medium-low heat, melt the butter. Mix in chocolate chips. Add sweetened and condensed milk. Remove from heat and add vanilla. Pour and spread this over the layer of baked oats. Top with the remaining oat mixture, dropping in clumps over the chocolate.
Bake for 15 - 20 minutes. Cool before cutting into squares.