Slice the leeks and place them in a bowl of cold water for about 5 minutes.
drain the leeks and rinse them again in a colander, pat them dry and set them aside.
Slice 1 1/2 pounds baby yellow potatoes in half and place them in a bowl; toss with 1 tablespoon extra virgin olive oil and a little bit of sea salt and pepper to taste.
arrange the oil-coated potatoes on a parchment-lined baking sheet and bake them until they are fork-tender which will be about 15 to 20 minutes.
While the potatoes are cooking, add 1 1/2 tablespoons unsalted butter to a skillet and melt it over medium heat. Once the butter has melted add the sliced leeks with garlic and begin to caramelize them; this should take about 15 minutes.
Add the chopped rosemary and the roasted potatoes; toss everything together and serve immediately.
Notes
Store leftovers in the refrigerator in an airtight container for up to three days. Reheat leftover potatoes in a skillet on top of the stove or in the oven.Yukon Gold or larger yellow potatoes can be used in place of the baby potatoes. Cut them into chunks that are 1 1/2 to 2 inches in size.