Melt the chocolate chips using the double-boiler method (Use a double boiler or a small pot with a glass or stainless steel bowl that fits the pot’s circumference. Fill the pot with enough water so that the bowl or double boiler is above but not touching the water. Place the chocolate in the bowl over the pot and bring water to a gentle simmer. Stir as the chocolate melts. Remove from heat when chocolate is nearly 100% melted. Any remaining chips will melt from the heat of the melted chocolate. Let cool slightly.).

In a medium bowl, whisk together the flour, cocoa, instant espresso, baking powder, and salt. Set aside.

Cream together the butter and the brown sugar with an electric mixer until the mixture is light and fluffy. Add the vanilla, and beat the mixture again. Carefully add the melted chocolate, and gently mix until combined.

Add the flour mixture to the butter-chocolate mixture, alternating with the milk. Cover the bowl and refrigerate the cookie dough for an hour or overnight. You’ll be rolling balls between your hands, so the colder (not frozen) the dough is, the easier it will be.

Remove the dough from the refrigerator. Preheat the oven to 350ºF and line a baking tray with parchment paper. Form the dough into 1-inch balls.

Roll the balls of cookie dough in the plate of sifted, powdered sugar to generously coat them. Place them on the baking tray, about 2 inches apart. Bake the cookies for about 15 minutes, or until the cookies have crackled on top and flattened out a bit. Let cool slightly on the baking tray before transferring the cookies to a wire rack.