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| russet potatoes: 4 whole potatoes |
| onions (chopped): 1 cup |
| carrots (grated): 1 cup |
| white mushrooms (sliced): 1 cup |
| salted butter: 2 Tbl |
| 2% milk: 1/4 cup |
| lemon juice: 1 Tbl |
| Dijon mustard: 1 tsp |
| salt: 1 tsp |
| black pepper: 1/4 tsp |
| parmesan cheese (optional) |
Credit: Food.com