Place the sweet potatoes on a baking sheet and poke each one a few times with a fork. Bake for 40–50 minutes, or until very soft. Remove from the oven and let cool until easy to handle. Reduce the oven temperature to 350°F (180°F).
3. Step
Meanwhile, cook the bacon in a medium skillet over medium heat until crispy. Transfer to a paper towel–lined plate to drain.
4. Step
Pour out all but 2 tablespoons of bacon grease from the skillet. Add the onion to the skillet and cook over medium heat for about 5 minutes, or until soft and translucent. Add the thyme and rosemary, and cook, stirring, until fragrant, about 1 minute. Remove the pan from the heat and let the onions cool slightly.
5. Step
Scoop the flesh of the sweet potatoes into a large bowl, discarding the skins. Add the cream, egg, salt, and pepper, and stir to combine. Add the onions and Gruyère cheese, and stir to incorporate.
6. Step
Transfer the sweet potato mixture to a 9-inch square glass baking dish.
7. Step
Make the topping: In the same skillet, melt the butter over medium heat. Add the stuffing and stir until warmed through and slightly toasted, about 2 minutes.
8. Step
Sprinkle the crumbled stuffing evenly over the sweet potatoes. Crumble the bacon and evenly sprinkle on top.
9. Step
Cover the baking dish with foil and bake for 30 minutes, until heated through. If desired, remove the foil and broil on high until the topping is lightly browned, 1–2 minutes. Keep an eye on the casserole so it does not burn.
10. Step
Remove the casserole from the oven and garnish with fresh thyme. Let cool for about 10 minutes before serving.
