Set the Instant Pot to sauté and add the tablespoons of butter.

When the butter is melted, add the sliced onion and fry the onions for about 5 minutes stirring often until softened. Add the minced garlic and continue to cook for 1 minute or until fragrant, then turn off the Instant Pot.

Pour over the stock, add the kosher salt, fresh ground pepper, fresh chopped sage, and the sliced potatoes, stir to combine.

Close the lid and point the valve to the sealed position. Turn the unit on and cook on High Pressure for 1 minute. Natural release for 3 minutes, then quick release the remaining pressure in the Instant Pot.

While the potatoes cook quickly, flash fry the sage if desired in some olive oil until crispy.

Remove the lid and add the heavy cream* and grated Gruyere cheese. Gently stir until the cheese has melted.

Transfer to a lightly greased gratin dish or baking dish.

Sprinkle the top layer of potatoes with the grated parmesan cheese and broil until the grated parmesan begins to brown.

Remove from the oven and serve! Sprinkle the top with crispy fried sage leaves or fresh sage leaves that have been chiffonade or sliced thinly.