Preheat the oven to 180°C bake.
Spread the peanuts onto a baking tray in a single layer.
Roast for 9–10 minutes, or until lightly golden and fragrant.
Allow the peanuts to cool slightly, then transfer them to a food processor.
Blend until the peanuts break down into crumbs, then continue processing until they form a smooth peanut butter. This can take several minutes depending on your machine.
Add the salt and oil, if using, and blend again until combined.
Taste and adjust the seasoning if needed.
Transfer to a clean jar and store in the fridge.