Preheat oven to 180C°/350°F (160°C fan) and grease 2 x 22cm/9" cake pans with butter, then line the base.
Sift flour, cocoa, baking powder and baking soda into a large bowl. Add Sugar and salt. Whisk briefly to combine.
Add eggs, milk, oil and vanilla. Whisk well to combine until lump free - about 30 seconds.
Add boiling water and whisk to incorporate. The batter is VERY thin.
Pour batter into cake pans.
Bake
for 35 minutes or until a wooden skewer inserted into the centre comes
out clean.
Cool for 10 minutes, then turn out onto wire racks upside down.
Cool completely before frosting. I frosted the cake with Niamh's Chocolate Buttercream frosting.