In a double boiler or in the microwave*, melt chocolate chips and sweetened condensed milk together until smooth. Set aside to cool while preparing cookie dough.

Cover and refrigerate for two hours. Roll filling into 1-inch balls.

In a medium bowl, whisk together flour, cocoa powder, baking powder and salt.

In a large bowl, beat butter with an electric mixer until light and fluffy.

Gradually beat in 2 cups (7 3/4 ounces) of powdered sugar until well combined. Set aside remaining 1/2 cup powdered sugar in a shallow dish.

Beat in eggs and vanilla in three separate additions, until smooth. Stop to scrape bowl as needed.

Beat in melted chocolate until combined. Beat in flour mixture just until combined.

Cover and refrigerate dough for 2 hours. Don't skip this step.

Preheat oven to 350ºF. Line two large baking sheets with parchment paper.

Roll dough into 15 2-inch balls, 1 1/4 ounce each. Flatten each ball into a 3-inch disk. Place a fudge ball in the center of each disk and wrap dough around it, pinching edges together to seal. Roll dough balls generously in remaining powdered sugar.

Place dough balls three inches apart on prepared baking sheets. Bake until cookies puff up and tops are set, about 11-13 minutes. Transfer cookies to a cooling rack.