Spread flour on a baking sheet and bake at 350°F (175°C) for 5 minutes. Let cool completely.
In a mixing bowl, cream together softened butter, brown sugar, and granulated sugar until light and fluffy.
Mix in milk, vanilla extract, and salt until well combined.
Gradually stir in the cooled, heat-treated flour until fully incorporated.
Fold in mini chocolate chips gently, spreading them evenly throughout the dough.
Press the dough evenly into a parchment-lined 8x8 pan. Chill for at least 2 hours until firm.
Lift out of the pan and slice into bars using a sharp knife. Wipe knife between cuts for clean edges.