Place the thawed strawberries into a blender or food processor and blitz until smooth.
Pour into a medium pot and sprinkle over the gelatin powder, let sit for 5 minutes to allow the gelatin to bloom.
Add the sugar to the pot and place over a medium heat on the stove. Stir until the sugar has dissolved and the gelatin has melted.
Pour through a metal strainer into a bowl.
Line a 6-inch bottomless ring mold with aluminum foil on the bottom which comes up the sides tightly. Alternatively, you can use a 6-inch round silicone mold. Place into a flat baking tray. Pour the strawberry puree mixture. Freeze for at least 1 hour, covering the top with plastic wrap to prevent freezer burn.
To make white chocolate mousse:
Add the water to a small pot and sprinkle over the gelatin powder. Allow to sit for 5 minutes so the gelatin can bloom.
Place the white chocolate chips into a medium, heatproof bowl.
Pour 1/2 cup of heavy cream into a medium pot and set over a medium heat on the stove. Heat until gently steaming then remove from the heat and pour over the white chocolate chips in the bowl. Allow to sit for 5 minutes so the white chocolate melts and only then, stir together until smooth.
Heat the pot with the bloomed gelatin over a medium-low heat, stirring until the gelatin has melted. Pour this into the white chocolate cream mixture and stir thoroughly to combine. Set aside to cool to room temperature.
Place the remaining 2 cups of heavy cream in a large bowl. Whip until thick with soft peaks, being careful not to overwhip. Fold half of the cooled white chocolate mixture into this until well combined. Gently fold the remaining white chocolate mixture inches Immediately move onto the next step otherwise the mousse will start to set in the bowl.
Assembly before freezing:
Take an 8-inch round, bottomless ring mold and line the base with plastic wrap: Cut a large sheet of plastic wrap, set the ring mold on top of it and pull the plastic wrap up the outside of the ring mold, pressing together to adhere. Line the base with aluminum foil as well in a similar fashion. Set on a flat baking sheet. Alternatively, you can use an 8-inch round silicone mold, which you will not need to line.
Remove the frozen strawberry jelly from the freezer and pop out of the mold. If it is hard to remove from the mold, dip into a very wide, shallow bowl of hot water to help melt the edges so it can be removed. Set aside.
Pour half of the white chocolate mousse into the prepared 8-inch mold. Place the frozen strawberry jelly into the mold, then the chocolate cake on top. Cover with the remaining mousse.
Place into the freezer for 8-12 hours until completely set.
To make mirror glaze:
Place 1/4 cup of water into a small bowl and sprinkle over the gelatin powder. Set aside for 5 minutes to allow the gelatin to bloom.
Place the sweetened condensed milk, white chocolate and bloomed gelatin mixture into a tall heatproof container for example a wide mouthed mason jar, large Pyrex jug or similar.
In a medium pot, place the sugar, liquid glucose and remaining water. Heat on low, stirring until the sugar has dissolved.
Once the sugar has dissolved, increase the heat to medium and bring to 217 degrees F, using a thermometer to measure the temperature.
Once this temperature has been reached, pour this over the chocolate mixture in the tall container. Let stand for 5 minutes so the chocolate can melt.
Use a hand blender to blitz until smooth – make sure the wand of the blender is completely submerged in the mixture to prevent air bubbles forming in the mixture.
Let the glaze cool to room temperature then place into the fridge to chill until needed.
Remove the mousse cake from the freezer and, if using a silicone mold, pop it straight out. If using a ring mold, let it sit for 5-10 minutes to soften slightly then peel away the aluminum foil and plastic wrap from the base. Run a palette knife or butter knife around the edge of the cake in the mold to loosen then pop out of the ring.
Place the cake onto an inverted mug or a can set on a baking sheet.
Reheat the glaze in a microwave at 50% power in 10-20 second bursts until the edge has melted and the canter is wobbly. Stir together until smooth. Check the temperature – it needs to be 95 degrees F – if it is a bit too hot, just let it sit until it reaches that temperature. If it is too cool, microwave in 10-20 second bursts, stirring each time, until it reaches the correct temperature.
Scoop 1/3 cup of glaze into one small bowl. Scoop another 1/3 cup of glaze into a separate small bowl.
To one small bowl, add a drop of white food coloring and stir until smooth.
To the other small bowl, add a couple of drops of purple food coloring and a drop of red food coloring to get a deep purple-pink color.
To the tall container of glaze, add one drop of purple food coloring and one drop of red food coloring to get a pale pinky-purple color.
Pour the small bowls of glaze into the tall container of glaze. Stir together very briefly to only slightly marble them together. Immediately pour the glaze over the mousse cake in a circular motion, ensuring all the edges of the cake are covered. Let sit until the glaze has stopped dripping off the bottom edges. Once this happens, use a small, sharp knife to trim off any excess glaze from the bottom edge to make it look neat. Transfer to a serving plate and chill the cake for 1 hour before serving (serve chilled).