Sprinkle gelatin over cold water in small bowl; stir and let stand 1 minute to soften.
Add boiling water; stir until gelatin is completely dissolved. Let stand to cool.
Stir together sugar and cocoa in a large mixing bowl; add heavy cream.
Beat at medium-high speed until stiff peaks form; gradually pour in Baileys, vanilla, and gelatin mixture, beating continuously at high speed until well-blended and soft peaks form.
Let stand 5 minutes to thicken.
Spoon a tablespoon of mousse into 5 centimeters wide half dome silicone moulds. Use the back of a spoon to spread mousse mixture around moulds. Then fill with mousse and use a small offset spatula to even out the tops before freezing for 3 hours.
While the mousse is freezing combine lustre dust and crushed Oreos together.
Carefully take frozen mousse out of silicone moulds and roll around in gold Oreo crumbs. Place back in the freezer until ready to use.
Preheat a fan-forced oven to 160C (320F) or 180C (356F) for a conventional oven. Line a cupcake tin with cupcake liners.
In the bowl of a stand mixer fitted with the paddle attachment, add the cocoa powder, plain flour, salt, bicarb soda and sugar. Turn mixer on low speed and allow it to mix for a couple minutes to help everything combine well!(alternatively you may do this by sifting the ingredients together). Add the softened butter there is no butter visible and it's well incorporated into the dry.
Next, add milk and eggs in a jug and whisk until well combined.
Add wet ingredients to dry ingredients in a slow and steady stream until no dry ingredients are visible. Scrape down the bowl and mix for another 20 seconds.
Fill each paper 3/4 of the way (using an ice cream scoop to transfer the batter into the cupcake liners makes this a quick and easy process otherwise you can use two tablespoons). Sprinkle the tops with crushed Oreo cookies. Bake for 20-25 min or until a toothpick inserted comes out clean. Allow them to cool completely on a wire cooling rack before frosting.
Core the centre of each cupcake and fil with chocolate sauce.
Carefully place each frozen mousse on top of the cake.
Combine lustre dust and vodka/vanilla until very well combined. Use a teaspoon to splatter on mousse.
Use the gold lustre dust to paint mini Oreos and place on top of the mousse.