Serve with a side salad of your choice.
Preheat the oven to 325°F. Place the yams in the oven and bake for 40 minutes until slightly soft. Remove from the oven and let cool for about 10 minutes.
While the yams are cooking place the olive oil in a medium sauce pan over medium heat. Add the onion and cook for about 3 minutes.
Add the sage, peppermint, chicken stock, water, salt and pepper. Cover and cook for about 30 minutes and remove from the heat.
When the yams are cool, slice lengthwise and scoop out the flesh leaving the skins. Add the flesh to the pan with the soup. Cook for about 5 minutes and then puree until smooth. Add the milk and puree.
Reduce the heat to very low to keep the soup warm.
While the soup is keeping warm, place the bacon in a large skillet over medium-high heat. Cook on each side until brown but not crispy. Remove to a towel, pat dry and dice.
Slice the yam skins into a medium dice and add to the pan with the remaining bacon grease. Cook for about 5 minutes.
Add to the soup, stir and serve.