Heat-treat the flour by spreading it evenly on a baking sheet and baking at 350°F (175°C) for 5 minutes to kill any bacteria. Let it cool completely before using.
In a large mixing bowl, beat the softened unsalted butter, creamy peanut butter, light brown sugar, and granulated sugar together until creamy and smooth using a hand mixer or stand mixer.
Add the pure vanilla extract and milk to the mixture and continue to beat until fully combined.
Gradually add the heat-treated flour and salt to the wet ingredients, mixing on low speed until just combined. Do not overmix.
Fold in the mini chocolate chips evenly with a spatula.
Scoop the cookie dough into small balls or use as desired. Store in an airtight container in the refrigerator.
Enjoy immediately or chilled for a firmer texture.