Rinse the wild rice under cold water, then place it in a saucepan with the vegetable broth. Bring to a boil, reduce heat, cover, and simmer for 45 minutes until the rice is tender and most liquid is absorbed.

While the rice cooks, melt the butter in a large skillet over medium heat. Add the diced onion and cook for 4 minutes until softened.

Stir in the sliced mushrooms and minced garlic. Cook for 6 minutes until the mushrooms release their liquid and start to brown.

Pour in the heavy cream, then add the dried thyme, salt, and black pepper. Simmer for 3 minutes to thicken slightly.

Preheat the oven to 375°F. Combine the cooked wild rice with the mushroom cream mixture in a large bowl. Stir in half the shredded cheddar cheese.

Transfer the mixture to a greased 8x8 baking dish. Sprinkle the remaining cheese and the breadcrumbs evenly over the top.

Bake for 20 minutes until the top is golden and the edges bubble. Let it rest for 5 minutes before serving.