Balsamic beef stew with veggie mash

Name: Balsamic beef stew with veggie mash
Ingredients: 1 tbsp olive or rapeseed oil; 2 large onions, (325g), halved and sliced; 600g diced lean stewing beef; 2 garlic cloves, chopped; 10g dried porcini mushrooms; 2 tbsp balsamic vinegar; 2 tbsp tomato purée; 2 tsp vegetable bouillon powder; 1 tsp English mustard powder; 320g carrots, finely chopped; 200g large chestnut mushrooms, quartered; few fresh thyme sprigs; 4 x 80g portions broccoli, cut into florets; 750g swede, cut into chunks; 500g potatoes, cut into small chunks