Preheat oven to 175°C (347°F). Sift together all dry ingredients except sugar.

Grease a cake pan and line with parchment. Beat butter and sugar until cream-colored. Add eggs one at a time, beating ~1 minute each.

Fold in dry ingredients on low speed, then add milk and mix on low until smooth (batter will be thick, not runny).

Smooth batter into pan and bake 30-40 minutes (check after 35 — chocolate cake can overbake/dry out quickly).

Let cool 5 minutes in the pan, then remove to cool completely.

Melt chocolate (double boiler or microwave, 2-3 min) and let cool slightly.

Whip cream with powdered sugar; fold in melted chocolate while whipping until thick. Chill 30 minutes until firm.

Once the cake is fully cooled, trim the domed top and edges (~1cm), and slice the cake into 2-3 horizontal layers. Pulse the trimmings into crumbs.

Brush each cake layer with milk, then spread chocolate cream between layers and over the top/sides.

Coat the entire cake with the reserved cake crumbs mixed with sifted cocoa powder (this crumb coating is the cake's signature look, not plain cocoa dusting).

Refrigerate 8-9 hours before serving so the layers set.