Preheat oven to 400 degrees F. In a large bowl, whisk together the olive oil, mustards, lemon zest, lemon juice, and garlic. Add the potatoes and toss to coat with the mixture. Spread the potatoes on a rimmed baking sheet and sprinkle generously with salt.
Bake for 30 minutes. Toss the potatoes, return to the oven, and bake for 15 minutes, or until the potatoes are a deep golden brown and fork-tender.
Transfer the potatoes to a serving platter, squeeze the fresh lemon juice over them, and sprinkle with parsley. Serve hot.
