Step 1

Preheat the oven to 350˚. Line 2 baking sheets with parchment paper. For the cookies: Put the chocolate chips in a microwave-safe bowl and microwave at 50 percent power in 15-second intervals, stirring between each, until melted and smooth. Let cool slightly.

Step 2

Combine the flour, cocoa powder, baking powder, baking soda and salt in a medium bowl and whisk.

Step 3

Combine the butter, granulated sugar and brown sugar in a large bowl and beat with a mixer on medium-high speed until smooth and light, about 2 minutes. Add the egg, vanilla and melted chocolate and beat until well combined, about 30 seconds. With the mixer on low speed, beat in half of the flour mixture, then the buttermilk, then the remaining flour mixture until smooth. Mix in the pecans.

Step 4

Drop heaping tablespoonfuls of dough on the baking sheets about 2 inches apart. Bake, rotating the pans halfway through, until the tops of the cookies are puffed and the edges are set, 8 to 10 minutes. (Don’t overbake; you want the centers to stay fudgy.) Let cool 5 minutes on the baking sheets, then remove to a rack set over a separate parchment-lined baking sheet.

Step 5

For the glaze: Melt the butter in a small saucepan. Remove from the heat and whisk in the milk, cocoa powder and vanilla until smooth. Add the powdered sugar and whisk vigorously until smooth. Spoon the glaze over the cookies, letting it drip down the sides. Let the glaze set, about 1 hour.