Heat the extra virgin olive oil in a medium saucepan over medium heat. Add the minced garlic and cook for 1-2 minutes while stirring, or until it becomes fragrant. Add the butter beans to the saucepan and cook for 1-2 minutes or until the beans are heated through. Remove the saucepan from the heat and set aside to cool slightly.
Pour the garlic bean mix into a food processor bowl, add 3 tablespoons of milk and blitz until thick and creamy. Or if using an immersion/stick blender, leave the garlic white beans mix in the saucepan, add 3 tablespoons of milk and blitz until smooth and creamy. Set the garlicky white beans aside.
Cut the potatoes into 1 inch cubes and add them to a microwave-safe container. Add just enough water to cover the base of the container. Heat in the microwave on high for 6-7 minutes or until the potato pieces are soft in the centre when pierced with a fork. I prefer to steam my potatoes in the microwave, as they keep more nutrients this way. Otherwise, add the potatoes to boiling water, reduce to a simmer and cook for 15 minutes or until very soft. Drain the potatoes.
Mash the potatoes with either a masher or a fork until they are creamy and fluffy.
Add the butter bean mash, fresh chives, nutritional yeast and the remaining milk to the potatoes. Stir the mashed potato and beans together until combined. If your potato and white bean mash is very thick, add a splash more milk and stir to mix.
Serve hot as a side to your main meal, or if you are making it ahead, store it in the fridge and heat it in the microwave just before serving.