To prepare the cookies:

1. Preheat the oven to 400 degrees F.
2. Line two baking sheets with parchment paper. Set aside.
3. In the bowl of a stand mixer fitted with a paddle attachment, beat together the butter, vanilla extract, baking powder and sugar.
4. Add the large egg. Continue to beat until just combined. Slowly add flour 1/2 cup at a time alternating with the milk.
5. Scoop cookie dough a tablespoon at time onto the baking sheet, leaving 2 inches between scoops.
6. Using the bottom of a flat, greased glass, lightly press down on the scoops so that they are mostly flat.
7. Bake the cookies for 8-10 minutes. They will be thick and cakey. Do not bake them until fully brown.
8. Transfer the baked cookies to a cooling rack, and allow to cool completely.

To prepare the icing:

1. In a medium saucepan over medium-low heat, add the bittersweet and semisweet chocolate chips.
2. In a small saucepan over medium-high heat, bring the heavy cream to a boil.
3. Pour the boiling milk over the chocolate chips. Stir lightly to combine. Add the light corn syrup to the chocolate-milk mixture, and stir until smooth. Stir in confectioners’ sugar, and allow to cool slightly, about 5 minutes.

To finish the cookies:

1. Dip the flat bottom of each cookie into the chocolate icing. Transfer to a baking sheet, and allow to cool completely.
2. Spread additional chocolate onto the cookie until the thickness of the chocolate matches that of the cookie.
3. Allow the chocolate to set, then store at room temperature until ready to serve.