01 - Cream butter and brown sugar in 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 (2 tsp each), arrange on parchment-lined plate, and refrigerate until firm.
02 - Combine butter and dark chocolate in heatproof bowl. Microwave in 30-second intervals or melt over double boiler, stirring until completely smooth. Allow to cool slightly before proceeding.
03 - Beat granulated sugar, brown sugar, and eggs in large mixing bowl for 2 minutes until pale and creamy. Incorporate vanilla and melted chocolate mixture, blending until uniform.
04 - Whisk together flour, cocoa powder, baking powder, and salt in separate bowl. Gradually add to wet ingredients, mixing until thick, fudgy dough forms. Refrigerate 10-15 minutes for easier handling.
05 - Set oven to 350°F. Line two baking sheets with parchment paper.
06 - Portion 2 tbsp brownie dough per cookie. Flatten in palm, center chilled cookie dough ball, and encase completely with brownie dough, sealing edges securely. Repeat for remaining dough.
07 - Arrange cookies on prepared trays with adequate spacing. Bake 10-12 minutes until tops are set with crackled appearance. Avoid overbaking for ideal fudgy texture.
08 - Let cookies rest on baking sheets 10 minutes before transferring to wire rack. Cool to room temperature before serving.