01 - Cream the softened butter and brown sugar in a small bowl until light and fluffy. Blend in the milk and vanilla extract. Stir in the heat-treated flour and salt until fully incorporated, then fold in the mini chocolate chips. Form 12 small balls approximately 2 teaspoons each, arrange on a parchment-lined plate, and refrigerate while preparing the brownie cookie dough.
02 - Combine butter and chopped dark chocolate in a heatproof bowl. Melt using the microwave in 30-second intervals or over a double boiler, stirring until completely smooth. Allow the mixture to cool slightly before proceeding.
03 - In a large mixing bowl, beat granulated sugar, brown sugar, and eggs for approximately 2 minutes until the mixture appears pale and creamy. Pour in the vanilla extract and the cooled melted chocolate, mixing until thoroughly combined.
04 - Whisk together the flour, cocoa powder, baking powder, and salt in a separate bowl. Gradually add the dry ingredients to the wet mixture, mixing until a thick, fudgy dough forms. Refrigerate the dough for 10-15 minutes to improve handling.
05 - Set oven to 350°F. Line two baking sheets with parchment paper and set aside.
06 - Portion approximately 2 tablespoons of brownie cookie dough per cookie. Flatten each portion in the palm of your hand. Position a chilled cookie dough ball in the center and enclose it completely with the brownie dough, ensuring a tight seal. Repeat with remaining dough and filling.
07 - Arrange the stuffed cookies on the prepared baking sheets, leaving adequate space between each. Bake for 10-12 minutes until the tops are set with a crackled appearance. Avoid overbaking to maintain optimal fudgy texture.
08 - Let the cookies rest on the baking trays for 10 minutes to set, then transfer to a wire rack to cool completely before serving.