- Preheat oven to 400 degrees F. Butter 9x13 inch glass baking dish.
- Fill large bowl with cold water. Peel and slice each potato into 1/8-inch-thick rounds and place in bowl with water. Repeat with sweet potatoes.
- Combine cream, butter, and garlic in medium saucepan; bring to simmer. Remove from heat.
- Mix all herbs in small bowl.
- Mix sea salt and black pepper in another small bowl.
- Drain potatoes and pat dry with kitchen towels. Transfer half of potatoes to prepared baking dish, spreading out evenly. Sprinkle with half of salt-pepper mixture, then half of herb mixture. Sprinkle with half of the cheese. Repeat with remaining potatoes, salt-pepper mixture, herb mixture, and cheese. Pour cream mixture over gratin, pressing lightly to submerge potato mixture as much as possible.
- Cover gratin tightly with foil. Bake 30 minutes.
- Uncover and bake until top of gratin is golden and most of liquid is absorbed, about 25 minutes longer.
- Let stand 10 minutes before serving.
- NOTE: This can be made 6 hours ahead. Cover with plastic wrap and chill. Remove plastic wrap before baking.
|Prep Time: 30 minutes|
Cook Time: 1 hour
|-||1 1/2 pounds Yukon Gold potatoes|
|-||1 1/2 pounds sweet potatoes|
|-||2 cups heavy whipping cream|
|-||1/4 cup butter|
|-||2 cloves garlic, minced|
|-||1 tablespoon fresh rosemary, minced|
|-||1 tablespoon fresh sage, minced|
|-||1 tablespoon fresh thyme, minced|
|-||1 tablespoon fresh Italian parsley, minced|
|-||1 1/2 teaspoons sea salt|
|-||3/4 teaspoon freshly ground black pepper|
|-||1 1/4 cups Gruyere cheese, grated|