Preheat the oven to 400 degrees. Peel the sweet potatoes and cut them into medallions about 1/2 inch thick. Arrange them on a baking sheet lined with parchment. Brush the medallions with olive oil on both sides. Bake until just tender, about 20 minutes. Remove from the oven and set aside.
Keep the oven heated to 400. Arrange the bacon on a baking sheet lined with foil. On another baking sheet lined with parchment, arrange the onion slices and the head of garlic. Put the bacon on a rack in the top third of the oven and the onion and garlic on the bottom third. Cook for 25 minutes, switching the pans halfway through. If the onions start to get too browned, remove them from the pan but keep the garlic in until it is soft and the cloves easily pop out of their skin.
Put the cooked bacon and the onions in a blender. Squeeze the garlic cloves into the blender as well. Pulse until everything is about the same size and the mixture is nearly spreadable. Add the black pepper, maple syrup and the wine to the blender and pulse again a couple of times to combine. Taste and adjust seasonings if necessary.
Spoon 1 teaspoon of the jam onto each sweet potato medallion and place on a serving platter. Top with a teaspoon of creme fraîche or sour cream and garnish with your choice of herb. Grind additional black pepper over the medallions if desired.