Preheat your oven to 350°F (175°C). Spread the all-purpose flour evenly across a clean, rimmed baking sheet and bake for about 7 to 10 minutes until it reaches an internal temperature of 165°F (74°C).

Remove the flour from the oven and let it cool completely. Break up any clumps using a whisk.

Prepare your 9 by 13-inch rectangular baking pan by lining it with parchment paper, leaving some overhang for easy removal.

In a large mixing bowl, add the softened unsalted butter, packed light brown sugar, and granulated sugar. Beat together for about 3 minutes until light and creamy.

Pour in the vanilla extract and whole milk, continuing to beat on low speed until smooth and blended.

Gradually add the cooled heat-treated flour and salt. Mix on low until a soft dough forms, scraping the sides as needed.

Fold in the mini chocolate chips using a spatula until evenly distributed.

Transfer the dough to the prepared baking pan, spreading it evenly. Press firmly to create a smooth layer.

Refrigerate the pressed dough layer for about 30 minutes until firmer.

In a microwave-safe bowl, combine semisweet chocolate chips, creamy peanut butter, and coconut oil. Microwave in intervals, stirring until melted and smooth.

Pour the chocolate mixture over the chilled dough, spreading evenly. Tap the pan lightly to release air bubbles.

Cover and refrigerate for about 2 hours to set.

Remove the bars from the refrigerator, let sit for 5 minutes at room temperature. Use the overhanging parchment paper to lift out and place on a cutting board.

Warm a sharp knife under hot water, dry it, and slice the bars into 20 rectangles.