Preheat oven at 180°c – 360°F. Butter a 22 CM (8 inch) cake pan.
In a medium bowl sift flour, baking powder and cacao powder.
In a large bowl mixer add eggs, sugar, vanilla and salt, Whisk in a medium speed until light in color.
Reduce the speed to slow, to eggs mixture add melted butter, milk and gradually add the dry ingredients. When all well incorporate, give the cake mixture a quick mix and pour it in the prepared cake pan.
Bake in preheated oven 180°c for 25 minutes. When out of oven place cake on a wire rack to cool and remove the parchment paper.
To prepare the chocolate mousse: melt the chocolate in microwave for 1 minute, mix with a spatula until will melted, let it cool while prepare the whipped cream.
Whisk the whipped cream in a medium speed make sure the cream at room temperature, if it cold the chocolate will shrink. Whip until the cream coherent and the cream a little bit liquidy than usual because it is room temperature, don’t over whisk otherwise the cream will fall apart.
Add the cream to chocolate gradually and keep mix all together until you have a smooth chocolate mousse.
Halve cake layer horizontally using a long serrated knife. Layer cake, using a 1/2 cup mousse between layer, then frost top and sides with remaining frosting.
With a peeler grate dark chocolate until cover all the chocolate cake.Chill 2 hours before serving.