Dry roast rose petals and keep aside.
Next roast almonds, cashew, poppy seeds, melon seeds, pepper corns, fennel seeds on a slow flame for 2-3 mins.
Cool this and add a drop of rose water and add in grinder along with cardamon and rose leaves and make a powder of the mixture.
You can store this mixture in air tight container and keep for one month in refrigerator.
For making thandai take 1/4 cup of milk and if you want yellow color add a pinch of turmeric (or kesar) and add 1 tbsp of mixture made with sugar to taste and let it mix well.
Now add this along with chilled milk in a blender and mix well, serve chilled with some rose petals and nuts garnish.