In a large heavy-bottomed pot over medium high heat, cook bacon until golden brown then remove the bacon to a paper towel lined plate. Add onion and garlic to the bacon fat, cook until tender, about 4-5 minutes. When the veggies are tender, add in the thyme, salt and ground black pepper. Add potatoes, stock, and milk to the pot and bring the liquids up to a bubble. Reduce the heat to medium and simmer the potatoes until cooked through, about 8-10 minutes. When the potatoes are tender, puree the soup until smooth using a blender, food processor or immersion blender.
Adjust the seasoning as needed with salt and freshly ground black pepper and serve the soup in a bowl or mug topped with the cheese, reserved bacon, a sprinkling of scallions. (If your not serving the soup right away it will thicken as it get cooler so add another 1/2 -1 cup of water when warming it up to serve)