1¼ cups (106 grams) Dutch process cocoa powder, sifted
Instructions
In a small bowl, place ¼ cup (60 grams) cold water. Sprinkle gelatin over water, and let stand until dissolved.
In a tall-sided medium saucepan, heat sugar, cream, and ¼ cup (60 grams) water over medium heat, stirring constantly, until sugar dissolves and mixture starts to boil. Cook, without stirring, until an instant-read thermometer registers 215°F (102°C) to 220°F (104°C). (This will happen quickly and mixture will bubble up, so make sure you use the correct pan.) Remove from heat, and whisk in gelatin mixture and cocoa. Pour mixture through a fine-mesh sieve into a heatproof bowl, and let cool until instant-read thermometer registers 105°F (41°C) before using. (Temperature is key for this to work correctly. Do not let it get too cold or it will set too fast and will not coat completely, and if you use it too hot, it will be super thin on the cake and will melt your mousse.)
Recipe by Bake from Scratch at https://bakefromscratch.com/baking-school-depth-chocolate-mousse-cake/