Chop your choclate into small pieces or like thick chocolate shavings to make it easier to melt. Transfer into a larger heatproof bowl and add the hot water.
Whisk to combine the chocolate and water till it resembles a watery brown liquid.
Allow the chocolate mix to cool a bit and carefully pour into your blender. (Make sure it's not too hot, as hot liquids can build pressure in a blender). Blitz for 2 minutes on medium speed. This will create lots of air and bubbles.
Pour into your glass dessert jars and refridgerate for 6-8 hours till firm.
Notes
70% cocoa solids make this chocolate mousse set really well.