How to Make It
Preheat the oven to 325°. Line several baking sheets with parchment paper. In a medium bowl, whisk the flour with the cocoa powder, baking soda and salt.
In a medium saucepan, melt the unsweetened chocolate with the butter over low heat. Scrape the melted chocolate into a medium bowl and let cool. Stir in the granulated sugar and vanilla until blended, then mix in the eggs. Stir in the dry ingredients until a soft dough forms, then fold in the milk chocolate.
Roll slightly rounded teaspoons of the dough into 3/4-inch balls. Arrange the balls 2 inches apart on the prepared baking sheets and flatten them slightly. Bake the cookies for about 13 minutes, or until firm outside but still soft in the center; rotate the baking sheets halfway through. Slide the parchment paper with the cookies onto wire racks to cool.
In a small bowl, blend the peanut butter with the confectioners' sugar. Spread the flat side of half the cookies with the peanut butter filling, top with the remaining cookies and serve.