Beef bourguignon cottage pie

Name: Beef bourguignon cottage pie
Ingredients: 1 tbsp sunflower or vegetable oil; 200g pack bacon lardons; 900g braising steak, cut into 3cm chunks; 225g button mushrooms; 225g button onions or small shallots, peeled; 2 garlic cloves, crushed; 1 tbsp demerara sugar; 600ml red wine; 400g can beef consommé (or use 400ml/14floz beef stock); 1-2 tbsp cornflour, loosened with 1-2 tbsp red wine or water; 1kg medium, floury potatoes, preferably Maris Piper or Desirée, quartered; 50g unsalted butter; 100ml milk