1Heat the oven to 350°F and arrange a rack in the middle. Coat a 9-by-5-inch loaf pan with butter. Line the bottom and two sides with parchment paper. Butter the parchment paper, then dust lightly with flour, shaking out the excess.
2Sift the flour and baking powder together onto a piece of parchment paper. In a heatproof bowl, whisk together the cocoa and espresso powders. Add the boiling water and stir until smooth. Set aside to cool, about 5 minutes.
3In the bowl of a stand mixer fitted with the paddle attachment, beat the butter, sugar, and salt on medium-high speed until light and fluffy, about 3 minutes. Beat in the eggs 1 at a time, beating well after each addition. Scrape down the sides of the bowl with a rubber spatula occasionally. Mix in the cocoa mixture and the vanilla. With a rubber spatula, gently fold in half of the dry ingredients until almost fully incorporated. Fold in the remaining dry ingredients and the chocolate chips just until the batter is smooth and the dry ingredients are incorporated.
4Pour the batter into the prepared pan and smooth the top. Bake until a toothpick inserted into the center comes out clean, about 1 hour.
5Let the cake cool in the pan on a wire rack for 5 minutes, then unmold the cake and peel off the parchment. Turn the cake top-side up and let it cool completely (cover the cake with a slightly damp kitchen towel so the outside doesn’t dry out). Just before serving, dust the top with powdered sugar.