1/4 cup (25 grams) unsweetened Dutch-processed cocoa powder
1/4 cup (60 ml) boiling hot water
1 1/2 cups (180 grams) cake flour
1 teaspoon (4 grams) baking powder
1/2 teaspoon (2 grams) salt
1 cup (225 grams) unsalted butter, at room temperature
1 1/4 cups (250 grams) granulated white sugar
1 1/2 teaspoons (6 grams) pure vanilla extract
4 large eggs, at room temperature
2 tablespoons milk, at room temperature
Preheat your oven to 350 degrees F (180 degrees C) and place the oven rack in the center of the oven. Butter, or spray with a non stick vegetable spray, a 9 x 5 inch (23 x 13 cm) loaf pan. Line the bottom of the pan with a piece of parchment paper.
In a small bowl mix the cocoa powder into the boiling water until the cocoa powder has dissolved and is smooth. Let cool to room temperature.
In a separate bowl, sift or whisk the cake flour with the baking powder and salt.
In the bowl of your electric mixer, fitted with the paddle attachment (or with a hand mixer), beat the butter until smooth. Add the sugar and vanilla extract and beat, on medium high speed, until light and fluffy (about 5 minutes). Add the eggs, one at a time, beating well after each addition. Scrape down the sides and bottom of your bowl as needed. Beat in the cooled cocoa mixture. With the mixer on low speed, add the flour mixture (in two additions) along with the milk (in one addition) and mix only until combined.
Scrape the batter into the prepared pan and smooth the top with an offset spatula or the back of a spoon. Bake for about 55 to 65 minutes or until a toothpick inserted into the center of the cake just comes out clean.
Remove the cake from the oven and place on a wire rack to cool for about 15-20 minutes. Run a spatula or knife around the inside of the pan and then remove the cake from the pan, peel off the parchment paper, re-invert, and cool completely on a wire rack.