Peel and cube the sweet potatoes and the Yukon gold potatoes. Scrub the new potatoes and cut into cubes.
Place all the potatoes into a large saucepan and add enough lightly salted water to cover. Bring to a boil and cook for 3 minutes. Drain thoroughly.
Spread the potatoes in a single layer on a large nonstick baking sheet.
Drizzle the potatoes with olive oil and sprinkle with tarragon, salt and pepper.
In a preheated 425-degree oven, roast the potatoes until browned and crisp, about 25 minutes. Serve immediately. Goes well with roast chicken or pork.
NOTE: Instead of tarragon, you can use 1 tsp. each of dried thyme and dried rosemary.
You can also add 4 whole leeks or chopped onion in the boiling water for 7-10 minutes until just tender, in Step 2. Chop the leeks after boiling.