Preheat the Oven: Set your oven to 350°F (175°C).
Make the Crust: In a large mixing bowl, combine the flour, brown sugar, and softened butter. Beat at medium speed until the mixture resembles fine crumbs, about 2 to 3 minutes. Press this mixture evenly into the bottom of an ungreased 13×9-inch baking pan to form the crust.
Prepare the Turtle Layer: In a small saucepan over medium heat, melt ⅔ cup butter with ½ cup brown sugar. Stir constantly until the mixture bubbles throughout, then continue for another 30 to 60 seconds. Remove from heat.
Assemble the Layers: Evenly distribute the pecan halves over the crust. Pour the hot brown sugar mixture over the pecans.
Bake: Transfer the pan to the oven and bake until the surface is fully bubbly, approximately 18 to 20 minutes.
Add the Chocolate Topping: Once baked, remove the bars from the oven and immediately sprinkle milk chocolate chips over the top. Allow the chips to melt for 2 to 3 minutes, then gently swirl the chocolate with a knife or spatula.
Cool and Slice: Let the bars cool completely in the pan for about 30 minutes. Once cooled, slice into 48 pieces with a sharp knife.