Preheat the oven to 350°F(177°C). Grease 8 ½ * 4 ½ inch (21,5*10,5cm) loaf pan and line the bottom and sides with parchment paper, about 2 inches(5 cm) of overhang on each side. If you like, you can grease and flour the dish instead of parchment paper.
Place the butter in a small pan and melt it halfway over medium heat. Take it from the heat and stir until it is all melted. The butter cools easily and doesn’t cook the eggs when they are added.
Place the flour, cocoa powder, baking powder and salt if using in a large mixing bowl and stir with a whisk. Set aside.
Place the eggs and sugar in a medium bowl and stir with a whisk until just combined.
Add in the melted butter, milk and vanilla extract, mix until combined.
Pour the wet ingredients into flour mixture and stir with a whisk/spoon. Once almost combined add the hot water until combined.
Pour the mixture into the pan and bake for 39 minutes or until a toothpick comes out clean that is inserted in the center. Few moist crumbs are fine. Let the cake cool in the pan for 20 minutes. After you remove from the pan, let it cool for 20 minutes on a wire rack before slicing.