Beef Bourguignon with Caramalised onion and potato mash

Ingredients for caramelized onions 
4 tablespoons unsalted butter
4 tablespoons olive oil 
1.5kg chopped onions (about 10 cups) 
3/4 teaspoon sugar
3/4 teaspoon salt 
1/2 teaspoon pepper   
Ingredients for the Potato mash 
2.5kg maris piper potatoes, peeled and cubed (1 inch)
4 teaspoons salt, 
divided 1 cup whole milk 
3 tablespoons unsalted butter 
1/2 teaspoon pepper   
 
Ingredients for Beef Bourguignon: 
3 teaspoons olive oil 
1kg diced steak pieces 
200g smoked bacon, 
sliced 500g onions,
sliced 500g closed cap mushrooms 
3 garlic gloves sliced 
2 tablespoons tomato purée 
bottle red wine , Burgundy is good     
 
1.     Prepare the vegetables by slicing 2 x medium onions and peeling and dicing the carrots. 
2.     Add the carrots to a pot of warm water and boil on a medium heat until carrots begin to soften then turn heat off. 
3.     Heat a large casserole pan and add 1 tablespoon Olive oil. Season the beef with salt and pepper and fry until golden brown, about 3-5 minutes, then turn over and fry the other side until the meat is browned all over, adding more olive oil if necessary. Do this in 2-3 batches if necessary, transferring the meat to a colander set over a bowl when browned.
4.     In the same pan, fry the sliced bacon, sliced onions, mushrooms and garlic until lightly browned. Mix in the tomato purée and cook for a few minutes, stirring into the mixture. This enriches the bourguignon and makes a great base for the stew. Then return the beef and any drained juices to the pan and stir through. 
 5.     Pour over the wine and about 100ml beef stock water so the meat bobs up from the liquid, but isn't completely covered. Bring to the boil and use a spoon to scrape the caramalised cooking juices from the bottom of the pan - this will give the stew more flavor. Drain off the carrots and add to casserole. 
 6.     Heat oven to 150C/fan 130C/gas 2. Then cook casserole for 3 hrs. If the sauce looks watery, remove the beef and veg with a slotted spoon, and set aside. Cook the sauce over a high heat for a few mins until the sauce has thickened a little, then return the beef and vegetables to the pan.