A personal take on cocoa powder: it's underrated. I always add a tablespoon or two of it to my chocolate desserts as I find it brings a richer and more concentrated flavor without the unnecessary sweetness.
Once cooled the glaze will solidify and resemble cream patisserie. This is warmed over a bain marie just till it melts (28°C to 30°C is the ideal temperature for use here) and strained through a fine sieve (a chinoise or coffee filter works a treat) to remove the bubbles and attain a smooth shine, the way glazes should be.
The Archilles' heel was my mousse: To ensure it set well I added extra gelatine which probably wasn't mixed thoroughly enough into the mousse: instead of setting, it sank and seeped out when the gateau was sliced, and with it sank my heart.