Method

• 1.
  Place cocoa and chocolate in a large heatproof bowl. Bring milk and 70ml water to the boil in a small saucepan over high heat. As soon as it boils, pour onto cocoa and chocolate and stir until smooth. Set aside at room temperature to cool for 30 minutes.
• 2.
  Preheat oven to 165°C/145°C fan-forced. Grease a 19.5cm-long x 11cm-wide x 11cm-deep loaf pan with cooking oil spray and line base and sides with baking paper.
• 3.
  Place flour, ¼ tsp fine salt and the bicarb in a medium bowl and set aside.
• 4.
  In a stand mixer fitted with the paddle attachment, beat butter and sugars on medium speed for 5 minutes, or until fluffy. Add eggs one at a time and beat on medium, ensuring fully combined before adding the next. Reduce speed to low and add cocoa mixture until streaky.
• 5.
  Remove bowl from mixer and sift over flour mixture. Fold flour mixture through until no streaks remain. Spoon into prepared pan and smooth top. Bake for 1 hour 10 minutes, or until a skewer inserted into the centre comes out with a few moist crumbs (internal temperature is a great way to test big, dense cakes like this – aim for 95°C on a kitchen thermometer). Cool in pan on a wire rack for 10 minutes (see recipe notes) before turning out. Invert and gently unmould cake onto a wire rack, remove paper and cool completely.
• 6.
  For the chocolate glaze, combine all ingredients with a pinch of fine salt in a medium heatproof bowl. Place over a saucepan of simmering water (don't let base of bowl touch the water) then stir until melted and combined. Pour over cake and quickly help it spread using an offset spatula. Set aside to set.
• 7.
  Cut into desired slices to serve.