Pre-heat your oven to 400 degrees.
Heat a cast-iron skillet or large pan over medium heat and add the pancetta. Cook for 5-6 minutes until browned and crispy. Using a slotted spoon, transfer the pancetta to a paper towel-lined plate to drain.
In a medium saucepan/pot, melt 1 tablespoon of butter. When melted add the minced shallots and garlic and sauté for 2-3 minutes until the shallots have softened. (Be careful not to burn the garlic!) Add the cream, sage, thyme and salt to the saucepan and heat until it is just simmering. Simmer very gently (you don’t want the cream to boil EVER, people) for 10-15 minutes to allow the flavors to infuse.
While your cream is simmering, prepare the sweet potatoes. Peel the potatoes and slice them in 1/8-inch discs. If you have a mandolin, please use it (carefully!). You want your discs to be as even in width as possible so that they cook evenly. Briefly set the potatoes aside.
Remove the sage and thyme from your cream, and taste the mixture. Add a little more salt if necessary and season with fresh ground pepper.
Pour ½ cup of the cream into a shallow baking dish. Add one third of the sweet potatoes to the dish in an even layer. Add another ½ cup of the cream, ¼ cup grated Parmesan and half of the pancetta.
Add a second layer of potatoes, cream, Parmesan and pancetta. Top with the remaining potatoes, and pour the remaining cream over the top of your gratin. Cover the baking dish tightly with foil and bake for 50 minutes or until the potatoes are very tender when pierced with a sharp knife.
While your gratin is in the oven, prepare the crunchy topping. Heat the butter in a large pan. When melted add the Panko and stir until the breadcrumbs are well-coated. Continue cooking, stirring constantly, until the Panko is golden brown. Transfer the toasted Panko to a bowl to cool. When cool, mix in the grated Parmesan and smoked paprika.
After 50 minutes, remove the foil from your gratin and add the topping in an even layer. Return the gratin to the oven for another 10-15 minutes until the top is crispy and browned and most of the liquid has been absorbed.
Sprinkle the gratin with freshly chopped sage and allow it to rest for 10 minutes before serving.