Add yogurt, chilled water, rose syrup, and cardamom powder to a blender and blend for about 30 seconds until the mix is smooth and frothy on top. Note: You can adjust the consistency of your lassi by adding more or less water.
Refrigerate until ready to use. Pour it into a tall glass and garnish with crushed dried rose petals. Serve chilled.
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Notes
Which yogurt to use: I prefer whole-milk yogurt for creamy results, but you can also use 2%-fat. I don't recommend using fat-free yogurt in this recipe. If using Greek yogurt, increase the water to ½ cup.
Rose Syrup: Use Rooh Afza for the classic taste and color. For an all-natural version, look for a rose syrup without any food coloring. Keep in mind that the lassi will be light in color.
Water: The amount of water used in this recipe yields a lassi that's thinner than a typical smoothie. If you prefer a thicker lassi, reduce or skip the water.
Sweetness: Rose syrup is pretty sweet and enough to sweeten the lassi. If you prefer a sweeter lassi, add a teaspoon of sugar.
Make it vegan: Use cashew yogurt instead of dairy yogurt to make this lassi vegan. And don't forget to check the rose syrup label to ensure it's vegan.
Note: The nutrition facts below are my estimates and have been manually entered for rose syrup based on the available product labels. If you follow any diet plan, I recommend cross-checking with your preferred nutrition calculator.