Caribbean sweet potato salad

1 large russet potato, peeled & quartered
1 large sweet potato, peeled & quartered
1 cup corn kernels
1 teaspoon Dijon mustard
2 tablespoons lime juice
3 tablespoons chopped fresh cilantro
1 clove minced garlic
3 tablespoons canola oil
1/2 teaspoon salt
1/4 teaspoon pepper
1 cucumber, peeled, halved lengthwise, sliced into thin half-rounds
1/2 red onion, sliced thin
1/4 cup finely chopped dry-roasted unsalted peanuts

1. Put the russett potato pieces into a large saucepan, and cover with salted water. Bring to a boil then lower heat and cook for 5 minutes at medium. Add the sweet potato pieces and cook an additional 20 minutes. Test each potato to see if cook (slightly firm but not breaking apart). Add corn kernals and cook 30 seconds more. Quickly drain in a colander. Fill the saucepan with cold water (a few ice cubes wouldn't hurt) and return potato/corn mixture to the cold water for 5 minutes (this stops the cooking process on the potatoes).
2. In a large bowl, combine the mustard, lime juice, cilantro and garlic; whisk. Slowly add the oil while whisking; add salt & pepper to taste (about 1/2 teaspoon salt and 1/4 teaspoon pepper).
3. Drain the cooled potato/corn mixture in a colander again. Now cut the potatoes into 1-inch cubes. Add the potatoes, corn, cucumber & onion slices to the vinaigrette. Mix well and serve chilled with a sprinkling of chopped peanuts.