In a pot over medium heat, bring all the base ingredients to boil, stirring occasionally. Once it starts boiling, reduce the heat to between low and medium, stirring constantly until the mixture thickens up very well. This will take anywhere between 10-15 minutes.
Remove and place onto a Pyrex bowl that's 9 x13 inches. Cover with plastic food wrap and let in cool at room temperature for 20 minute. Then place the bowl in the fridge to cool down more for 45 minutes.
Meanwhile, chill the heavy whipping cream in the freezer for about 10 minutes. Remove and whip the cream until it starts to get firmer, adding in the sugar gradually until the whip cream is firm. Cover and place in the fridge to chill until the base is ready.
When the base is ready, remove the plastic food wrap and top the base with the fresh cream. Then spread out the whipping cream in sections so you can be able to spready it out easily without any hassle.
Top the whipping cream generously with the processed pistachios, covering it entirely. Place in the fridge and let it chill overnight or for at least 6 hours. The longer the better.
To prepare the syrup, bring the sugar and water to boil. Once it starts boiling, let it boil for 7 minutes and then add in the lemon juice. Boil for another 1-2 minutes and then add in the rose and orange blossoms water. Stir well and then remove from heat. Cover and let it cool in room temperate until it's ready to be served with the dessert.