Finely chop the chocolate.
Place the double cream in a pot over medium heat and remove once it's almost to a boiling point. Make sure it doesn't start boiling!
Pour the hot cream evenly on top of the white chocolate and allow to sit for 5 minutes, without stirring.
Once the 5 minutes are up, use a whisk to slowly incorporate the two ingredients, with circular movements, from small to big circles.
Add the finely ground pistachios and mix together. You can drain the ganache if you want a finer texture, or keep it as it is for a crunchy one.
Pour the ganache in the tart shell, on top of the raspberry jelly and transfer back to the fridge until completely solid (or overnight).
Decorate the tart with chopped pistachios and rose petals or rose buds.
For a perfect cut, dip a knife in hot water and wipe dry before slicing the tart.