With their buttery flavor and texture, Yukon Golds create a rich, full-bodied backdrop for ribbons of anise-scented fennel, sweet cipollini onions, and olives.
Heat a medium skillet over medium-high heat. Add oil and garlic, and cook for 2 minutes. Add potatoes, onions, and red-pepper flakes. Cook until onions are golden, about 7 minutes.
Add stock, and season with salt and pepper. Bring to a simmer, cover, and cook until potatoes and onions are tender, about 10 minutes. Remove potatoes and onions with a slotted spoon. Reserve 1/2 cup cooking liquid.
Combine reserved liquid, vinegar, 1/2 teaspoon salt, and pepper. Pour over warm potatoes and onions. Stir in olives, and let cool completely.
Add fennel and parsley, and combine. Season with salt and pepper. Top with Parmesan.
To ensure maximum flavor, toss potatoes with dressing while they're still warm.