In a large mixing bowl, cream together the butter, brown sugar, and granulated sugar until light and fluffy. Add the vanilla extract and salt, mixing until combined. Gradually stir in the heat-treated flour, alternating with the milk, until a smooth dough forms. Fold in the mini chocolate chips.

Step 2: Press the Dough into a Pan

Line an 8×8-inch baking dish with parchment paper. Press the cookie dough mixture evenly into the bottom of the pan, smoothing the top with a spatula. Place in the refrigerator to chill while preparing the frosting.

Step 3: Make the Vanilla Frosting

In a separate bowl, beat the butter until smooth. Gradually add the powdered sugar, followed by the heavy cream or milk, vanilla extract, and a pinch of salt. Continue beating until the frosting is light and fluffy.

Step 4: Frost and Chill

Spread the vanilla frosting evenly over the chilled cookie dough base. Return to the refrigerator and allow the bars to set for at least 1 hour before slicing into squares.

Step 5: Serve and Enjoy

Cut the bars into squares and serve chilled for a firm texture or allow them to sit at room temperature for a softer bite.