Sauté the onions, garlic, salt and thyme with oil or broth until soft and browning. Abut 5 minutes. Set aside.
Make the sauce by putting all ingredients into a blender and blending until nice and smooth.
Layer in a square dish (9 x 9 or 8 x 8 works) as follows:
½ of the sliced potatoes
½ of the creamy sauce
½ of the onion mix
2 tablespoons of parmesan, optional
Last ½ of the sliced potatoes
Last ½ of the creamy sauce
Last ½ of the onion mix
Swirl to mix in a bit
Sprinkle another 2 tablespoons of parmesan on top, optional
Sprinkle extra thyme, optional
Cover loosely with foil.
Bake covered for 35 minutes.
Take off the foil and bake another 35 minutes, until potatoes are cooked through.
If you don’t have a high speed blender, soak the cashews overnight to soften them. You can also boil them for 20-25 minutes if you forget. Another method is using a coffee or spice grinder to grind them dry (not soaking) into a very fine powder.