Puff Pastry Tart with Onion, Mustard and Cheese

Recipe steps

Prepare the mustard cream

In a bowl, mix the cream, mustard, pepper, a pinch of salt (not too much, the cheese is already salty) and 80 g of Gruyère. Preheat the oven to 180°C (convection: 170°C).

Prepare the base

Unroll the pastry on its parchment paper, placed on a baking sheet. With the tip of a knife, score a border of 1.5 to 2 cm without cutting through the pastry, then prick the center with a fork: the border will puff up, the center will stay flat. Brush the border with the egg yolk mixed with water.

Add the toppings

Spread the mustard cream in the center, keeping it within the border. Peel the onions, slice them into thin rounds (about 3 mm) and arrange them slightly overlapping.

Add butter and season

Scatter with diced butter, drizzle with a little cream (if you saved some) and add a turn of the pepper mill. The butter will help the onions turn golden instead of drying out.

Bake in the oven

Place in the lower part of the oven, 25 min at 180°C, until the border is puffed and nicely golden and the onions have caramelized tips. Keep an eye on the last few minutes: an oven that’s too hot can burn the top onion slices.

Finish the recipe

Once out of the oven, snip the dill, sprinkle with the remaining Gruyère (20 g) and the Sbrinz, let rest for 2 min and serve.

Tips and variations

• Milder onions: sauté them for 5 to 8 min in a pan before placing them on the tart. They’ll be more tender, and the tart sweeter.
• Red or white onions: red ones add lovely color to the tart, white ones are more delicate. Spring onions also work well, when in season.
• More character: a Gruyère-Appenzeller mix in the cream, wholegrain mustard, or a few smoked lardons on top of the onions.
• Hearty vegetarian: add crushed walnuts or sautéed mushrooms.