This cake is more like bread in texture so it's quite dense but super tasty. To keep it moist and tender, take it out of the oven as soon as a toothpick inserted into the center of the cake comes out with moist crumbs and not completely dry, and serve the cake at room temperature. The important ingredient here is the coffee, so use a high quality brand that you like. For the best coffee flavor, it's better to weigh the instant coffee, you'll need 10 grams for this recipe, and then you can use either instant coffee granules or powder. I only had coffee granules and it was around 3 tablespoons. I use 1/4 cup more sugar than the original recipe to make it less bitter. Sift the cake with powdered sugar if you like.
Preheat oven to 325°F/160°C. Grease an 8½ x 4¼-inch loaf pan.
In a medium bowl, sift together flour, cocoa powder, baking powder, and salt.
Using a mixer fitted with the paddle attachment, beat butter and sugar on medium speed for 3 minutes until fluffy. Occasionally scrape down the sides and bottom of the bowl. Add eggs, one at a time, beating 1 minute after each addition. Mix coffee and milk in a small bowl and mix into the batter. Beat for 1 minute. The batter may look a bit curdled at this point, but that's ok. On low speed, beat in the flour mixture in 2 additions, mixing just until combined. Do not over mix.
Scrape batter into prepared pan and smooth the top. Bake for 45-60 minutes or until a skewer inserted into the center of the cake comes out with moist crumbs. If the cake is browning too much while baking, cover the top loosely with aluminium foil. Remove from oven and allow to cool completely on a wire rack. Serve cake at room temperature.
Store cake in an airtight container in the refrigerator for up to 5 days. Cake can be frozen for up to 2 months. Thaw overnight in the fridge.