Creamy Garlic Onion Potato Gratin

Ingredients

• 350 g Potatoes (peeled and sliced 2‑3 mm thick (use a mandoline for uniformity))
• 1 medium Onion (thinly sliced 2‑3 mm)
• 30 g Unsalted butter (room temperature)
• 18 g Garlic, minced (about 3 cloves)
• 5 g All‑purpose flour (approximately ½ tablespoon)
• 100 ml Whole milk (room temperature)
• 20 g Parmesan cheese, grated (about 3 tablespoons)
• 2 g Salt (approximately ½ teaspoon, adjust to taste)
• 100 g Mozzarella cheese, shredded (enough to cover the top; use low‑moisture for best melt)
• 5 g Fresh parsley, chopped (for garnish)

Instructions

1. Slice potatoes

   Peel the potatoes and slice them into uniform 2‑3 mm rounds using a mandoline or sharp knife.

   Time: PT5M

2. Slice onion

   Peel and slice the onion thinly (2‑3 mm).

   Time: PT3M

3. Pre‑cook potatoes in microwave

   Arrange a single layer of potato slices in the microwave‑safe dish, add a splash of water (just enough to create steam), cover loosely, and microwave on high (≈700 W) for 5 minutes until the potatoes are about 80 % done.

   Time: PT5M

4. Sauté garlic

   In a saucepan, melt the butter over low heat. Add the minced garlic and cook gently for 2 minutes, stirring constantly, until fragrant but not browned.

   Time: PT2M

   Temperature: low heat (≈120°C)

5. Make roux

   Sprinkle the flour over the melted butter and garlic, stirring continuously for 1 minute to form a smooth paste.

   Time: PT1M

   Temperature: low heat

6. Create cream sauce

   Gradually whisk in the milk, then add the grated Parmesan and salt. Continue stirring over medium heat for about 2 minutes until the sauce thickens and coats the back of a spoon.

   Time: PT2M

   Temperature: medium heat (≈80°C)

7. Layer the gratin

   In the baking dish, arrange a layer of pre‑cooked potatoes, then a layer of onion slices. Pour a portion of the cream sauce over the layers. Repeat until all ingredients are used, ending with a generous drizzle of sauce on top.

   Time: PT5M

8. First bake

   Place the dish in a pre‑heated oven at 200°C (392°F) and bake for 20 minutes.

   Time: PT20M

   Temperature: 200°C

9. Add mozzarella and finish baking

   Remove the dish, sprinkle the shredded mozzarella evenly over the top, and return to the oven. Bake for an additional 10 minutes, or until the cheese is melted, bubbly, and lightly golden.

   Time: PT10M

   Temperature: 200°C

10. Garnish and serve

    Remove the gratin from the oven, let it rest for 5 minutes, then sprinkle chopped parsley over the surface. Slice and serve while warm.

    Time: PT5M

Nutrition Facts

Calories

260

Protein

10 g

Carbohydrates

30 g

Fat

12 g

Fiber

3 g

Ingredient Substitutions

• Instead of Potatoes: sweet potatoes, yukon gold potatoes
• Instead of Onion: shallot, leek
• Instead of Unsalted butter: margarine, olive oil
• Instead of Garlic, minced: garlic powder (1 tsp)
• Instead of All‑purpose flour: cornstarch (2 tsp), gluten‑free flour
• Instead of Whole milk: unsweetened almond milk, soy milk
• Instead of Parmesan cheese, grated: Pecorino Romano, grated Asiago
• Instead of Salt: sea salt, kosher salt
• Instead of Mozzarella cheese, shredded: provolone, sharp cheddar
• Instead of Fresh parsley, chopped: cilantro, chives

Equipment Needed

• Chef's knife
• Cutting board
• Microwave‑safe dish
• Saucepan or skillet
• Wooden spoon or spatula
• Whisk
• Grater
• Measuring spoons
• Baking dish (≈9×9 in)
• Oven
• Oven mitts

Critical Steps — Do Not Skip

• Microwave the potatoes just until 80 % cooked – overcooking makes them mushy.
• Thicken the cream sauce to a coat‑the‑back‑of‑a‑spoon consistency; under‑thickened sauce will be runny after baking.
• Cover the potatoes with enough sauce before baking to prevent drying.
• Watch the final mozzarella bake to achieve a golden crust without burning.

Chef Tips from the Video

• Use a mandoline for perfectly even potato and onion slices.
• Pat the sliced potatoes dry after rinsing to avoid excess water in the dish.
• For extra flavor, add a pinch of nutmeg to the cream sauce.
• Let the gratin rest 5 minutes after baking; this makes slicing cleaner.

Troubleshooting

Storage

Refrigerator: Cool to room temperature, then cover and refrigerate for up to 3 days.

Freezer: Wrap tightly with foil and freeze for up to 1 month. Reheat in oven at 180°C until hot.

Room temperature: Do not store at room temperature for more than 2 hours.

Make-Ahead Tips

• Prepare the cream sauce up to step 6 and store it in the fridge for up to 24 hours.
• Assemble the layered gratin (without mozzarella) a day ahead, cover, and refrigerate; bake when ready.
• If freezing, assemble, cover tightly, freeze, then bake directly from frozen adding 10‑15 minutes to the bake time.