Use a mesh strainer to strain the raspberry puree and remove all seeds.
Add this seedless raspberry puree and sugar in a saucepan and cook on medium heat until you have a thick "syrup-like" consistency.
While the puree is cooking, add gelatin and water (or lemon juice) in a small bowl and let it sit for about 2 minutes until you end up with a "gel-like" mixture.
Now, pour the gelatin mixture into the raspberry mixture and mix until thoroughly combined.
Let this mixture cool down to room temperature. You can speed up the process by popping the saucepan in the fridge for 10 minutes but be careful since the gelatin will start to set fairly quickly.
While the raspberry mixture is cooling down, whip heavy cream in a cold mixing bowl until soft peaks form. Add red/pink food coloring, if you like.
Now, gently, fold the whipped cream into the raspberry mixture with a spatula and mix until just combined. DON'T OVER-MIX or else the texture of this mousse will totally change.
Let's put it all together now... Cut out small square brownie pieces and place them at the bottom of your serving cup. Use the back of a spoon to press the brownie pieces down at the base of the cup.
Spoon the raspberry mousse on top of the brownie, leaving about a 1 inch gap at the top.
Cover the serving cup with saran wrap and chill in the refrigerator for 5-6 hours until the mousse sets.
Prior to serving, spread a few teaspoons of raspberry jam or preserve on top of the mousse. Top it off with fresh raspberries and shredded white chocolate. Enjoy!
Notes
Read all my tips above.
Leftovers can be stored in a sealed container in the fridge for up to 3 days.