Preheat the oven to 350°F (175°C) and grease a loaf pan.
In a large bowl, whisk together the flour, cocoa powder, and sugar.
Add the melted butter, eggs, milk, and vanilla extract to the dry ingredients.
Mix until a smooth, lump-free batter forms. Do not overmix.
Pour the batter evenly into the prepared loaf pan.
Bake for 45–55 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs or clean.
Allow the cake to cool in the pan for 10–15 minutes, then transfer it to a wire rack to cool completely before slicing and serving.