Preheat the oven to 400 degrees F.On a large baking sheet, toss together the potatoes, olive oil and a pinch each of salt and pepper. Transfer to the oven and roast 20 minutes or until the potatoes are fork tender. Using a potato masher or a fork, gently press down on the potatoes, smashing them to about 1/4 inch thickness.Mix together the butter, garlic, and thyme. Drizzle the butter over the potatoes and return the potatoes to the oven and roast another 20-25 minutes or until golden and crisp. During the last 5 minutes of cooking, add a thin slice of brie to each potato and roast until melted. Arrange the warm potatoes on a serving plate and drizzle with truffle oil. Top with sage and peppercorns. Enjoy!