Preheat oven to 375 degrees. Spray a 12-cup muffin pan with cooking spray.
Thinly slice the potatoes into approximately 1/16th inch-thick slices with a mandoline or by hand with a sharp knife.
Combine the butter, olive oil, garlic, thyme, rosemary, salt and pepper in a large bowl.
Add the potatoes and toss until evenly coated.
Layer the potato slices in the prepared muffin pan, filling each cup to the top. Drizzle with any remaining butter/oil combination.
Bake for 45-50 minutes or until the tops are golden brown and the centers are tender. Rotate the pans once as ovens may have hot spots.
Let stand in the pan for 5 minutes. Carefully remove to a serving platter and garnish with fresh herb sprigs.
