Fill a small pot with water and chopped carrot. Bring to a boil. Boil 4 to 5 minutes, until fork tender. Then drain and set aside.(If you'd prefer, you can steam the carrot instead of boiling.)
In a high speed blender, combine 1 cup water, boiled carrot, raw cashews, lemon juice, kala namak (black salt), and Dijon mustard. Blend until completely smooth, stopping to scrape down the sides if necessary.(If you don't have a high speed blender, see notes for tips.)
Put blender mixture into a medium-sized pot. Bring to a low medium heat, stirring constantly to make sure it doesn't clump at the bottom of the pot. Cook for about 5 minutes, while the sauce condenses and thickens. Once it has the texture of gravy, remove from heat.
Stir 2 Tablespoons of non-dairy milk into the sauce and a generous pinch of salt. If you like, add an optional sprinkle of cayenne pepper. (Or you can add it as a final garnish when serving over vegan eggs benedict or air fryer asparagus.)
The sauce will continue to thicken as it cools. If needed, stir in one or two more Tablespoons of non-dairy milk before serving.
Notes
Tips for a standard blenderIf you don't have a high speed blender, you will need to help it with the raw cashews. You have three options.
Soak the raw cashews in water for at least a half an hour. Then drain and add them to the blender.
Boil the raw cashews with the carrots to soften them. Then drain and add them to the blender.
Grind dry raw cashews in a clean coffee grinder until it becomes the texture of flour. Then add it to the blender.
Halving the recipe?If you halve the recipe, be aware that the sauce will take about half the time to thicken in the pot on the stove.Storage & reheating tipsKeep leftovers in a covered container in the refrigerator. It will continue to thicken as it cools. It will keep for about 4 days.To reheat, microwave at 30 second intervals, stopping regularly to stir, until it comes up to temperature. Or you can reheat on the stove at a low medium heat, stirring constantly.The sauce will have thickened in the refrigerator & while reheating. Add another splash of non-dairy milk and stir.This sauce also freezes well in a freezer-proof container. When you're ready to use it, move it to the refrigerator to thaw before reheating.