Peel your potatoes and dice them and load the potatoes into the slow cooker with half the butter or margarine, salt, pepper, and mixed herbs. Allow to slow cook for 90 minutes on high to create soft mashed potatoes.
Whilst the potatoes are cooking in the slow cooker, do your stew prep work. Peel and dice carrots and onions. Wash and quarter your mushrooms. Slice your bacon rashers into chunks.
When the slow cooker is done, put the potatoes to one side in a suitable bowl and add the milk and other half of the butter and mash to make mashed potatoes.
Then into the slow cooker add your beef and sauté for a couple of minutes with extra virgin olive oil and brown the beef on all sides. Transfer the beef to a plate.
Same again and sauté the onion, mushrooms, and garlic but this time with the butter. When the mushrooms are nicely coloured and the butter is melted, move them to a spare plate too.
Next add the bacon into the slow cooker with a little extra virgin olive oil and sauté for a couple of minutes to give bacon flavour to the slow cooker pot.
Take the slow cooker from the stovetop and move to the slow cooker unit. Then add to the bacon the carrots, beef, tomato puree, tablespoon of the just cooked mash, red wine, beef stock, seasonings, and seasonings. Cook for 3 hours on high.
When the 3 hours are up add in garlic mushrooms, stir and add in a little extra mash to make it extra creamier if not creamy enough already.
Slow cook for a final hour before serving with leftover mashed potatoes.