In a medium pot or Dutch oven, heat a drizzle of EVOO over medium-high heat. Add bacon and cook until crispy. Remove bacon with a slotted spoon to a paper towel-lined plate and reserve. Drain off excess bacon fat from the pot and add butter. When it is melted, add the onion and cook until softened, about 5 minutes. Sprinkle flour into the pot and cook with a wooden spoon for 1 minute. Whisk in the chicken stock and bring to a bubble. Cook until slightly thickened, about 2-3 minutes.

Whisk in mashed potatoes, then stir in the cheddar cheese with a wooden spoon and cook until the potatoes are hot and the cheese is melted.