Preheat oven to 400°. Cook olive oil and butter in a skillet over medium heat, stirring constantly, 3 to 4 minutes or until butter begins to turn golden brown. Remove butter mixture from heat, and add peeled potatoes, tossing gently to coat.
Spread potatoes in a single layer in a 15- x 10-inch jelly-roll pan.
Bake at 400° for 40 to 45 minutes or until potatoes are golden brown and tender, stirring twice. Transfer potatoes to a large serving bowl, and toss with lemon juice, chopped fresh thyme, salt, and pepper until well coated. Serve potatoes immediately.