Oyster poutine

Mushrooms, oyster, torn into pieces	1 pound
Sweet potato fries, frozen	7 ounces
Oil, olive	¼ cup
Butter	2 tablespoons
Flour	2 tablespoons
Milk	¾ cup
Salt

1. Preheat the oven to 425°F. 
2. In a 3-quart baking dish, toss the mushrooms with the sweet potato fries and oil; bake for 45 minutes. 
3. In a saucepan, melt the butter, stir in the flour, and cook, whisking, until golden, about 5 minutes. 
4. Whisk in the milk and cook, whisking, until thickened, about 3 minutes; season with salt. 
5. Spoon the gravy over the mushrooms. 
6. Top with cheese. 
7. Broil until golden.