Preheat your oven to 180C and line a large baking tray with baking paper.
Spread the nuts over the tray in a single layer and place in the oven to roast for 8-10 minutes (keep an eye on them and don't let them burn!). This brings out the flavours and also releases the oils from the nuts, making them easier to blend.
If using peanuts or hazelnuts, you will need to remove their skins at this point. You can do this by rubbing between tea towels.
Remove from the oven and let the nuts cool for a while before adding to a high speed blender or food processor and pulse. At first the nuts will grind down, then, a thick paste will form. You can stop and scrape the sides down if needed. Keep pulsing until a runny nut butter forms (the time this takes depends on the blender or food processor you're using).
Once the nut butter has formed, you can add the salt and cinnamon. If you want to add any sweeteners, it's important to note that any water-based substances will cause the nut butter to 'seize up' and thicken.