3 tablespoons extra-virgin olive oil

1 cup diced onion

1 cup diced carrots

1/2 cup sliced celery

8 ounces sliced mushrooms

3 garlic cloves, minced

1/2 cup red wine

1 teaspoon red wine vinegar

3 tablespoons tomato paste

2 cups vegetable broth

1 (15-ounce) can white beans, drained and rinsed

2 teaspoons chopped fresh thyme (or 1 tsp dried)

2 teaspoons chopped fresh rosemary (or 1 tsp dried)

1 tablespoon chopped fresh parsley (or 2 tsp dried)

1/2 teaspoon salt

1/4 teaspoon ground black pepper

1 bay leaf

1 1/2 cups frozen mixed vegetables

2 pounds russet or gold potatoes, peeled and chopped

3 tablespoons unsalted butter

1/4 cup sour cream (or plain Greek yogurt/milk/cream)

1/2 teaspoon salt

3/4 cup shredded sharp white cheddar cheese (optional)

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Boil potatoes in a large pot until tender, 10–15 minutes. Drain and set aside.
Heat olive oil in a large skillet over medium heat. Add onion, carrots, celery, and mushrooms. Cook 5 minutes. Add garlic and cook 1 minute.
Add red wine and vinegar. Stir and cook until mostly evaporated, about 4 minutes.
Add tomato paste, broth, beans, thyme, rosemary, parsley, salt, pepper, and bay leaf. Bring to a boil, reduce heat, and simmer for 20 minutes until thickened. Remove bay leaf and stir in frozen vegetables.
Preheat oven to 350°F (177°C). If not using an oven-safe skillet, transfer filling to a greased 2.5–3-quart baking dish.
Mash warm potatoes with butter, sour cream, and salt. Fold in cheese. Spread over vegetable filling.
Bake for 30 minutes. Broil for 1–3 minutes until top is golden. Let cool 5 minutes before serving.

To make ahead: refrigerate cooked filling and mashed potatoes separately. Assemble and bake the next day, thinning potatoes with a bit of milk before spreading.
Substitute mushrooms with another can of beans if preferred.
Replace red wine with extra broth and vinegar if avoiding alcohol.
Use leftover mashed potatoes to save time.
Can be frozen up to 3 months; thaw before baking.