Preheat your oven to 350°F (175°C) and prepare the pan.
Cream the softened butter and sugar together until light and fluffy.
Add the eggs, one at a time, mixing well after each addition.
Mix in the vanilla extract until well combined.
Sift together the flour, cocoa powder, baking powder, and salt in a separate bowl.
Gradually add the dry ingredients to the wet mixture, alternating with the milk.
Mix until just combined; do not overmix.
Pour the batter into the prepared pan and smooth the top.
Bake in the preheated oven for approximately 60-70 minutes, or until a toothpick comes out clean.
Let the cake cool in the pan for 15 minutes before transferring to a wire rack.