Preheat the oven to 400°F. Line a baking sheet with parchment paper. Add the sweet potatoes, drizzle with olive oil, add the chili powder and season with salt and black pepper. Toss to coat, then arrange in a single layer. Bake for 40 to 45 minutes, tossing halfway through, until the sweet potatoes are tender and browning at the edges.

Add the broth and dried shiitakes to a medium saucepan and place on high heat. Cover with a lid, bring to the boil and then reduce the heat to low and simmer for 20 minutes. Remove the shiitakes from the saucepan and set aside. Transfer the broth to a bowl.

Return the saucepan to the stove, add the butter and melt it over medium heat. Add the shallots and cook, stirring often, for 2 to 3 minutes, until softened. Add the garlic and thyme, and cook for 1 minute. Sprinkle in the flour and cook for 1-2 minutes, stirring constantly. Add the warm broth, whiskey (if using), tamari, miso, and pepper. Stir, then bring to a boil over high heat. Reduce the heat to medium and cook for 5 minutes, stirring often.

Transfer the mixture to blender or use a handheld immersion blender and blend until smooth. Return to the stove and cook over medium heat for another 5 minutes or until thickened. Set aside.

Thinly slice the rehydrated shiitakes. Melt the butter in a skillet (frying pan) over medium-high heat, then add the shiitakes and cook until golden, about 2 minutes. Add the garlic, tamari, and pepper. Stir, then immediately remove from the heat to prevent burning.

Divide the sweet potato fries among four individual bowls. Top with crumbled feta, gravy, and sautéed shiitakes. Sprinkle with sliced scallions and serve.