Preheat oven to 400 degrees F (200 degrees C). Place potatoes into a large roasting pan and drizzle with an olive oil. Sprinkle with salt and pepper mix to coat potatoes with salt and olive oil. Roast in the preheated oven for 30 minutes. Meanwhile pour 1 Tablespoon olive oil into a large skillet over medium heat and cook shallot and mushrooms, until soft, that will take about 6-8 minutes. Season to taste. Stir potatoes in the baking dish; mix cooked mushrooms with potatoes. Return to oven and bake for another 15-20 minutes, until potatoes are soft.