Preheat oven to 400 degrees F. Prepare a baking sheet with parchment paper.Put cubed sweet potatoes in a mixing bowl, drizzle olive oil over the potatoes, sprinkle, Herbes de provence, and salt (and pepper if desired, I usually add the pepper before serving). Mix until the sweet potatoes are well coated. Spread out in one layer on prepared baking sheet and put into preheated oven. Using a baking spatula, scrap any remaining oil-spice mixture from the bowl onto potatoes on baking sheet. Bake for 30-40 minutes, taking out to turn potatoes over halfway through (I do this at 15-20 minutes into baking). Remove from oven when potatoes are tender (not mushy, you can test with a fork). If I have a few larger pieces, I will bake these until 40 minutes, just monitor when you are at 30 minutes baking time, everyone's oven may vary but 30 minutes should be enough time. Add additional salt and pepper at serving, if desired. Enjoy!