Bring 1 quart water to a boil in a medium pot. Remove from heat, add 1 ounce rose petals and stir well to submerge. Steep for 5 minutes, stirring 2 to 3 times. Meanwhile, mix a pinch of beetroot powder with 1/2 ounce hot water and whisk until dissolved. Strain petals. While the water is still hot, mix in the beetroot liquid and 1/2 ounce rose water. Let cool before using.
In a small saucepan, combine 6 ounces rose concentrate, 2 ounces milk (your choice), and sweetener (such as brown simple syrup) to taste. Heat over medium heat until steaming hot (but not boiling), stirring frequently. Remove from heat and blend with an immersion blender until frothy. Pour into a cup. Garnish with rose petals along one side.
Recipe by Ashley Jaffe, a cofounder of Blank Slate Tea in New York City.