Preheat your oven to 350°F (175°C).
Grease a 9x5-inch loaf pan with butter or cooking spray and dust with flour.
In a medium bowl, whisk together flour, baking powder, salt, and cocoa powder.
In a large mixing bowl, cream the softened butter and granulated sugar together for 3-5 minutes until light and fluffy.
Add eggs one at a time, mixing well after each addition, then stir in vanilla extract.
Gradually add the dry ingredients to the butter mixture, alternating with whole milk, mixing until just combined.
Pour the batter into the prepared loaf pan and smooth the top.
Bake for 60-70 minutes, checking for doneness with a toothpick.
Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.