Line a 9-inch square pan with heavy duty aluminum foil, grease with softened or melted butter. Set aside. Preheat oven to 350 F degrees.
Make the fudge: Melt butter and chocolate on a heavy-bottomed pan, add condensed milk and salt. Stir until smooth, set aside.
Cream butter and sugar until light and fluffy; add egg and vanilla, mix.
In a separate bowl, combine flour, oats, baking soda and salt, mix well and add to the creamed butter.
Spread 1/2-2/3 of batter in the prepared pan. Pour fudge, spreading evenly on top then spoon remaining batter over fudge. Bake for about 25 minutes.
Cool for about ten minutes on a wire rack before cutting into bars. Enjoy!