Preheat oven to 350°F.

Arrange the thick-cut bacon on a rimmed baking sheet lined with aluminum foil and cook until crispy, about 25-30 minutes; make sure to rotate the bacon halfway through cooking to cook evenly. Remove the bacon when crispy and transfer the strips to a plate or platter lined with paper towels to absorb excess drippings. Set the thick-cut bacon aside.

Adjust the oven to 375°F.

Wash and rinse the potatoes, peel them, and shred the potatoes using a box grater. Wrap the shredded potatoes in a paper towel and/or a large cheesecloth or kitchen towel, and squeeze out as much water as you can.

Shred the onion using a box grater, then use the same method to remove as much moisture as possible. I transferred onions into a fine-mesh sieve and, using the back of a tablespoon, pressed out as much water as I could. Set aside.

Mince garlic and parsley and set aside.

Grate one cup of smoked Gouda and one cup of Gruyere cheese.

Transfer the shredded potatoes, onions, and minced garlic and parsley to a large mixing bowl, and add 1 1/4 cups heavy cream, melted butter, and cheeses (reserve a little of the cheese for the topping).

Add sea salt and freshly cracked black peppercorns and mix thoroughly.

Place parchment lotus cups into a muffin pan, and fill each cup with the au gratin mixture.

Place the muffin pan on the middle rack of the preheated oven and bake for 30-40 minutes at 375°F. With 5 minutes remaining, top each cup with more cheese and continue to bake until the potatoes are golden brown.

Remove from the oven and top each cup with thick-cut bacon; just before serving, top each cup with green onion and serve.