Preheat the oven to 350 degrees F. Grease a 9 by 13-inch pan
Cream together the brown sugar, sugar, and butter. Add the eggs and mix until well mixed.
Fold in the old fashion oats. Once the oats are combined mix in the pecans. Reserve 2 cups of the oats mixture and set aside. Add the flour to the remaining oat mixture and mix in until the flour is mixed in all of the way.
Pat the remaining oat mixture into the prepared pan. Place in the preheated oven and bake for 10 minutes.
While the crust is baking make the chocolate fudge filling. Combine the chocolate chips, sweetened condensed milk, and butter. Melt over medium-low heat, stirring often until the mixture is melted.
Once the crust has baked 10 minutes remove from the oven and spread the chocolate fudge over top. Sprinkle the remain oat mixture over top of the chocolate fudge. Place back into the oven and continue to bake for 23 to 25 minutes or until the bars are set and the oats are lightly browned.
Remove and cool on cooling rack.