Step 1

Preheat oven to 375°F and liberally grease a 9x12-inch casserole dish with butter.

Step 2

Heat olive oil and the 1 tablespoon of butter in a large pan over medium-low heat. Add onions and cook until soft and translucent, about 5-8 minutes.

Step 3

Meanwhile, bring cream, garlic, rosemary, and thyme to a boil in a medium saucepan over medium heat, removing it from the heat as soon as it reaches a boil.

Step 4

Arrange 1/3 of the potatoes in the prepared casserole dish, overlapping slightly. Season liberally with salt and pepper and top with half of the onions and 1/4 cup of cheese.

Step 5

Repeat, layering another third of the potatoes, more salt and pepper, and the rest of the onions and another 1/4 cup of cheese.

Step 6

Top with the last third of the potatoes and season with salt and pepper again.

Step 7

Strain the cream from the saucepan to remove herb sprigs and garlic and pour liquid over potatoes.

Step 8

Cover dish with foil and bake until potatoes are tender when pierced with a knife, about 45 minutes. Remove foil, top dish with remaining cheese and continue to bake until golden and bubbly, about 15-20 more minutes.

Step 9

Let rest 10 minutes before serving. Enjoy!