Sweet Potato and Yukon Gold Bake

Ingredients

• 2 tablespoons extra virgin olive oil
• 4 cups sliced onions
• 1 teaspoon fresh thyme, minced
• 1/2 teaspoon salt
• 2 pounds of sweet potatoes, mixed in color if available, peeled and sliced into 1/8-inch thick rounds
• 2 pounds Yukon Gold potatoes, peeled, and sliced into 1/8-inch thick rounds
• 2 tablespoons melted butter
• 1 teaspoon of salt
• 1/4 teaspoon black pepper
• Sprigs of fresh thyme

Directions

1. Warm the olive oil in a large, heavy pot over medium heat. Add the sliced onions and turn them in the oil, then reduce the heat to medium low and cover the pot. Cook for 15 to 20 minutes, stirring now and then, until the onions are fully softened while you slice the sweet potatoes and Yukon Golds.
2. Raise the heat to medium high and continue cooking the onions without the lid until they turn golden brown. Take the pot off the heat, then mix in the salt and thyme. Peel and slice all the sweet potatoes and Yukon Golds, aiming for pieces that are as even as possible.
3. As you work, drop the slices into a bowl of water to keep them from discoloring. If you are using purple sweet potatoes, put those slices in a separate bowl of water, since their color can run.
4. Drain the potato slices and transfer them to a bowl. Spread the caramelized onions across the bottom of a 9x12 rectangular or oval casserole dish in an even layer.
5. Set the sweet potato and Yukon Gold slices over the onions in tidy rows.
6. Brush the top with melted butter, then season with salt and pepper. Cover the dish with foil and bake at 400 degrees F for 45 minutes, until the potatoes are tender all the way through. Take off the foil and return the dish to the oven for 15 minutes, until the edges are browned and crisp.
7. Finish with a little more salt and pepper. Add fresh thyme sprigs on top, and serve right away.