In a large Dutch oven over medium heat, add olive oil and onions and saute until translucent. 

Add potatoes, stock, salt, and pepper and turn heat up to high to boil. 

Boil potatoes until you can easily put a fork into them and you can see the starch coming off of them – this helps thicken the soup.

While the potatoes are boiling, heat a skillet to medium high and saute bacon pieces until crispy – drain grease on a paper towel. 

In a separate bowl, add milk and flour and whisk together. When potatoes are done boiling, turn off the heat and add the milk and flour mixture. Stir the soup. The soup will start to thicken as the milk warms up. 

When the soup starts to thicken, stir in half of the shredded cheddar cheese (save the rest for topping). 

Top with additional cheese, bacon, and chives.