Potato and Broccoli au Gratin

Pro tips

• Slice potatoes uniformly thin (1/8 inch) so they cook evenly; use a mandoline for consistent results and faster prep.
• Precook potatoes in salted water for 5–7 minutes until just tender—they'll finish cooking in the oven and stay firm rather than turning to mush.
• Bring the cream sauce to a gentle simmer before pouring over layers; a cold sauce prolongs cooking time and may leave raw spots.
• Top the gratin with a thin, even layer of grated cheese 10 minutes before the end of baking to achieve a crispy, golden crust without overbaking the layers below.

Substitutions

• Heavy cream → whole milk mixed with butter (roux-based sauce); slightly less rich but still creamy
• Gruyère → sharp cheddar or emmental; adjust seasoning as aged cheddar is sharper
• Broccoli → cauliflower or green beans; cook times vary slightly

Storage & make-ahead

Refrigerate leftovers in an airtight container for up to 3 days. Reheat covered in a 325°F oven for 15–20 minutes until heated through, or use a microwave at 50% power to avoid drying out.

Equipment

mandoline or sharp knife for uniform potato slicing · 9×13 inch baking dish or gratin pan

Can I prepare potato and broccoli au gratin ahead of time?

Yes. Assemble the gratin completely, cover with foil, and refrigerate for up to 24 hours. Bake directly from the fridge, adding 10–15 minutes to the baking time.

Why is my gratin watery or curdled?

Overcooking breaks down the cream sauce. Keep oven temperature at 375–400°F and bake only until the potatoes are tender and the top is golden. Undercook the potatoes slightly before layering to avoid mushiness.

What cheese works best for au gratin?

Gruyère or sharp cheddar melts smoothly and adds depth. Emmental and fontina also work well. Avoid fresh cheeses; aged varieties brown better and prevent a gluey texture.

How thick should I slice the potatoes?

Slice potatoes 1/8-inch thick with a mandoline or knife. Too thick and they won't cook through; too thin and they break apart during layering.

Can I use frozen broccoli?

Thaw and pat dry thoroughly to prevent excess moisture. Fresh broccoli is preferred for texture, but frozen works in a pinch—reduce baking time by 5–10 minutes.