One Potato, Two Potato

The dual-potato approach is what makes this side worth your time. Sweet potatoes and waxy new potatoes have different starches, sugars, and textures, and layering them creates a side dish with unexpected complexity from a five-ingredient list.

Sweet potatoes bring moisture, deep orange color, and natural sweetness that balances the more savory new potatoes. The starchy new potatoes hold their shape and add structural body, keeping the gratin from collapsing into a sweet potato puree.

Skim milk in place of cream is the lighter touch. It thins the cooking liquid, doesn’t add fat, and lets the natural starches from the potatoes thicken the sauce as everything bakes together. The 10-minute uncovered finish at the end is what gets the top layer to brown lightly.

Pro Tips

• Slice the potatoes paper-thin (⅛ inch or less), thicker slices won’t cook through in the time given.
• Use a mandoline if you have one, hand-slicing varies in thickness and the gratin bakes unevenly.
• Pre-soak the new potato slices in cold water for 10 minutes to remove surface starch, this prevents them from sticking together during baking.
• Don’t lift the cover too early, the steam underneath cooks the potatoes uniformly.

Variations

• Add a sprinkle of grated Parmesan on top before the uncovered finish for a richer browned crust.
• Sub buttermilk for skim milk for a tangier flavor.
• Layer in a few sprigs of fresh thyme between the potato layers for an herbal note.