Peel the garlic and onion, wash the herbs and chop everything finely. Heat the olive oil up in a pan and add the garlic, onion, rosemary and sage. Fry at medium heat.
Chop the beetroot and apple into cubes. Slice the mushrooms and add everything to the pan. Cook until there is only little liquid left. Season it with salt, cinnamon and nutmeg. Add the bean paste and cranberries and stir well. Take it off the heat and let it cool down.
Now assemble your Wellington. Roll the puff pastry out on a flat surface and spread the cold sweet potato mash evenly on top, leaving a 2cm border. Add the vegetable mix on top of the pastry and roll it up. Brush the milk on top of the rolled up pastry and prick it with a fork. Bake it for about 40 minutes in the preheated oven, until it its golden brown. Let it cool a bit, than slice into equal pieces.