Chop your potatoes and carrots into even pieces and steam/boil until knife tender
Allow to cool enough for your blender, and blend alongside your nutritional yeast, olive oil, brine, cashews, cornflour and jalapenos (if desired). Add a splash of water to get your blender going - you can use the water you boiled your veg in
Then simmer on low heat in a saucepan until your desired consistency, season with salt
Notes
This will thicken up the next day, just simmer again on a low heat and add a touch of water to bring it back to your desired consistency.