Let's cook.
Preheat your oven to 375 degrees Fahrenheit and grease a 9x13 inch baking dish generously with the softened butter.
In a medium saucepan, combine the heavy cream, minced garlic, thyme, salt, and pepper over medium heat until it just begins to simmer.
Layer one-third of the sliced potatoes into the prepared baking dish in an overlapping pattern.
Pour one-third of the hot cream mixture over the potatoes and sprinkle with one-third of the grated Gruyère cheese.
Repeat the layering process two more times until all ingredients are used, ensuring the final layer is topped with the remaining cheese.
Cover the dish with aluminum foil and bake for 30 minutes.
Remove the foil and bake for another 25 to 30 minutes, or until the potatoes are fork-tender and the top is golden brown and bubbling.
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