Put the potatoes, carrots and onion into an oven proof dish and coat in olive oil.
Sprinkle over the dried herbs.
Cover with a lid or foil and bake until tender but not coloured. Mine took about 30 minutes but this will vary depending on your oven.
Remove from oven and allow to cool.
Once cool put all the vegetables in a food processor along with all the other ingredients except the walnuts.
Process until almost smooth.
Add the walnuts and pulse so they are broken into little bits. Do not process for too long as you want a bit of crunch left there.
If you have mini loaf pans then line one with cling wrap and spoon your pate in, pressing it down well. If you don't have a mini loaf pan then you can use any container you like. Bear in mind though that if you want to turn it out to slice you will need to line it with cling wrap. If you are happy just to spoon it out then don't worry.
Cover tightly with cling wrap and refrigerate for at least 2 hours although overnight is best if you want it to firm up enough to turn out and be sliceable.