01 - Cream the butter and brown sugar in a small bowl until light and fluffy. Blend in milk and vanilla. Stir in heat-treated flour and salt until fully combined. Gently fold in mini chocolate chips. Form 12 small balls (approximately 2 teaspoons each), arrange on parchment-lined plate, and refrigerate until firm.
02 - Combine butter and chopped dark chocolate in a heatproof bowl. Melt using microwave in 30-second intervals or over double boiler, stirring until smooth. Allow mixture to cool slightly before proceeding.
03 - Beat granulated sugar, brown sugar, and eggs in a large mixing bowl for approximately 2 minutes until mixture becomes pale and creamy. Incorporate vanilla extract and melted chocolate mixture, blending until uniform.
04 - Whisk together flour, cocoa powder, baking powder, and salt in a separate bowl. Gradually add dry ingredients to wet mixture, stirring until thick dough forms. Refrigerate dough for 10-15 minutes for easier handling.
05 - Set oven to 350°F. Line two baking sheets with parchment paper and set aside.
06 - Portion approximately 2 tablespoons of brownie dough per cookie. Flatten each portion in palm. Place one chilled cookie dough ball in center and enclose completely with brownie dough, pinching edges to seal. Repeat for remaining cookies.
07 - Arrange cookies on prepared trays, leaving space between each. Bake for 10-12 minutes until surfaces are set with characteristic crackle pattern. Avoid overbaking to maintain fudgy interior texture.
08 - Let cookies rest on baking sheets for 10 minutes to firm. Transfer to cooling rack and allow to cool completely before serving.