I made something similar to this recently. We must have enjoyed it because I went in that direction again. The boiled potatoes were flattened and roasted with butter and a sprinkling of powdered rosemary, thyme and salt.
For the sauce, I cooked cauliflower and raw cashews with a little water and “chicken” style seasoning, which basically consists of nutritional yeast mixed with various herbs, spices and salt. McKay’s Chicken Seasoning is the original but I used my homemade version.
I blended the cooked cauliflower and cashews, adding a dab of yellow mustard and water as needed.
The cauliflower sauce was delicious with the roasted potatoes as was the jalapeño chocolate sauce I made. We also enjoyed both sauces together on the potatoes.