Gratin is a French dish of thinly sliced potatoes baked in milk or cream. The term ombré means “shading.” This technique creates a smooth transition of color in the vegetable pattern, giving the dish a striking, elegant look. Using three groups of ingredients—for the base, the vegetables, and the sauce—this method turns seasonal vegetables into a festive phyllo-topped gratin despite its simple components.
For this oven-baked French gratin, you’ll need three groups of ingredients.
Ingredients for the base: store-bought phyllo dough – 16 sheets; butter – 120 g.
Ingredients for the vegetables: potatoes – 1 kg; sweet potatoes – 2; pumpkin – 900 g; beets – 2; Gruyère cheese (hard, dense, melts easily) – 800 g; salt – a pinch.
Ingredients for the sauce: eggs – 3; butter – 3 tablespoons; shallots – 30 g; garlic – 8 cloves; mustard – 4 tablespoons; bay leaves – 8; thyme (dried) – 2 tablespoons; nutmeg (ground) – a pinch; salt – 1.5 teaspoons; black pepper (ground) – a pinch.
Preparation
- Start by making the fragrant vegetable-and-cheese sauce. In a large pot over medium heat, melt the butter and add the chopped shallots, garlic, and whole black peppercorns. After the shallots soften (about 5 minutes), add the bay leaves, thyme, nutmeg, ground pepper, and salt. Simmer the sauce on low heat for 20 minutes, stirring occasionally, until it thickens slightly.
- Strain the seasoned cream through a fine sieve into a large bowl (you should have about 3 cups) and pour it back into the pot. In the emptied bowl, whisk the egg yolks with the cream: beat the yolks, then gradually add a spoonful of warm cream several times, whisking to combine. Reserve one cup of the cream for serving.
- Slice the unpeeled sweet potatoes very thinly (you can substitute regular sweet potatoes with regular potatoes), season with salt and pepper, and mix them in the pot with the warm cream.
- Layer the gratin to create the ombré effect. Cut the peeled beets in half, thinly slice them with a sharp knife, season with salt and pepper, and arrange them in two even layers in a greased baking dish so the slices slightly overlap. Evenly sprinkle about one and a third cups of grated cheese on top of the beets.
- Place the seasoned potatoes on top of the beets and cheese in two or three even layers, pressing down to avoid air pockets. Sprinkle the potatoes with the same amount of grated cheese.
- Season the chopped pumpkin with salt and pepper, layer it over the potatoes and cheese in two layers, and sprinkle with grated cheese.
- On top of the pumpkin and cheese, layer the potatoes in two or three layers and pour the remaining creamy mixture over the vegetables.
- Place the prepared ombré gratin—potatoes, sweet potatoes, pumpkin, and beets—on the middle rack of the oven, with a baking sheet on the rack below to catch any drips. Bake the gratin with the creamy sauce for one hour in a preheated oven at 190°C (375°F), until the vegetables are tender.
- Crumple the phyllo sheets into folds and brush each with melted butter to form 8 strips.
- After an hour, remove the vegetables from the oven, cover them with the crumpled phyllo strips, brush the top layer with melted butter, and bake until the phyllo is golden brown for another half hour, increasing the heat to 220°C (428°F).
- Before slicing, let the aromatic gratin rest for 30 minutes to allow the liquid to absorb and make it easier to cut into portions.
- Meanwhile, heat the reserved cream over medium heat for 2 minutes, season with salt and pepper, and serve it alongside the gratin.
Cooks who have made this ombré gratin with potatoes, sweet potatoes, pumpkin, and beets say it’s worth the effort—especially for a family dinner or a festive table. If you prefer a simpler version, reduce the number of vegetables.
Tips for the Perfect Ombré Gratin
- To ensure hard root vegetables become tender and creamy, slice them very thinly – a vegetable peeler makes this easy.
- You can prepare the sweet potatoes and pumpkin in advance, but slice the regular potatoes and beets just before assembling to prevent the potatoes from darkening and the beets from becoming mushy. Another option is to par-cook the firmer vegetables briefly before assembling.
