First you need to cook your potatoes and carrots. The most common way is too peel them, and boil until fork tender. I'm impatient so I microwave them. For the potatoes, I'll poke them a few times with a knife or fork. Then microwave on a microwave safe plate for 8 - 10 minutes flipping halfway through, or until the internal temp is around 200 F / 93 C. My microwave is 1000 watts by the way! So adjust accordingly.
Once cooked, cut the potatoes in half and let them cool down for a few minutes. You should be able to peel the skin off, but be careful, don't burn your fingers!
For the carrots, I'll peel them, and cut into chunks. Then add them and 1 - 2 Tbsp of water to a microwave safe dish, cover loosely, and microwave for 4 - 6 minutes, or until fork tender.
Then you simply need to blend everything in a high speed blender until smooth. Season to taste, adding anything you like to get it tasting good to you! If it feels too thick, add some more plant milk until it's at a consistency you like.
I like to add Citric Acid for extra tang, as well as some oil for a better texture. But that is totally optional! I tested the sauce with and without Turmeric and found that if you add more than 1/2 tsp you can taste the turmeric, which I don't mind, but if you are sensitive to it, I would leave it out as it's not needed except to get a more vivid color.