Preheat the oven to 350ºF and grease a large cast iron pan with butter.
Peel and thinly slice your potatoes into about ⅛ inch slices. If you have a mandolin, this can help with uniformity.
In a medium bowl, mix together cream, ¼ cup parmesan, sage, rosemary, garlic powder, salt, and pepper until combined.
Add potato slices to the bowl in small batches to coat them completely in the cream mixture, then arrange the potatoes in a spiral pattern around the pan until all potatoes are used.
Pour any excess cream mixture over the potato slices, then cover the pan with tin foil and bake for 40 minutes.
Remove the pan from the oven, sprinkle the grated gruyere and Swiss cheeses over the potatoes, and return to the oven uncovered for another 10-15 minutes, until the cheese is golden brown and bubbling.
While the potatoes are on their second bake, cook the bacon using your preferred method (oven, microwave, stovetop, etc. - I prefer the microwave since it's fastest).
Chop the bacon into small pieces, and when the potatoes are done, sprinkle the bacon, the remaining parmesan cheese, and any other desired herbs on top to garnish.