Mushroom, Thyme & Gruyère Tart

20 minutes, plus 27-30 minutes baking and 5 minutes resting · Serves 4

a crisp mushroom, thyme and Gruyère tart made for a quiet autumn lunch

Golden pastry, thyme & rain outside.

A note from Essy: A crisp, golden tart for the sort of autumn lunch that quietly becomes early supper. The mushrooms are cooked until deeply browned and dry, then layered with thyme, Dijon and Gruyère. Keep the pastry cold and let the oven do the impressive part.

Ingredients

• 1 sheet ready-rolled all-butter puff pastry, approximately 320 g and 35 x 23 cm, kept chilled
• 1 medium egg, beaten with 1 tsp cold water
• 1 tbsp olive oil
• 15 g unsalted butter
• 400 g chestnut mushrooms, wiped clean and sliced approximately 5 mm thick
• 1 medium shallot, finely sliced
• 1 garlic clove, finely grated or crushed
• 2 tsp fresh thyme leaves, plus a few extra leaves to finish
• 1/2 tsp fine sea salt
• freshly ground black pepper
• 80 g crème fraîche
• 1 tsp Dijon mustard
• 100 g Gruyère, coarsely grated
• To serve, optional: a simply dressed green salad

Method

1. Heat the oven to 220°C conventional / 200°C fan. Put a heavy baking tray into the oven to heat. Unroll the chilled pastry on its baking paper and place it on a second, cool tray or board.
2. Using the tip of a small knife, score a 2 cm border around the pastry without cutting all the way through. Prick the centre all over with a fork, leaving the border untouched. Brush the border lightly with the beaten egg.
3. Slide the pastry, still on its paper, onto the hot baking tray. Bake for 10-12 minutes, until the border has risen and the centre is lightly puffed. Remove it from the oven and gently press the centre down with the back of a spatula, keeping the border intact. Reduce the oven to 210°C conventional / 190°C fan.
4. While the pastry bakes, heat the olive oil in a large frying pan over medium-high heat. Add the mushrooms and spread them out. Cook for 8-10 minutes, stirring only occasionally, until their released liquid has evaporated and the edges are deeply golden.
5. Lower the heat to medium. Add the butter and shallot, then cook for 3 minutes until the shallot is soft. Add the garlic and thyme and cook for 1 minute. Season with the salt and several turns of black pepper, then remove the pan from the heat. There should be no visible liquid left in the pan.
6. Stir the crème fraîche and Dijon together. Spread the mixture over the pressed centre of the pastry, staying inside the raised border. Scatter over 60 g of the Gruyère, spoon the mushroom mixture evenly on top, then finish with the remaining 40 g Gruyère.
7. Return the tart to the oven and bake for 17-18 minutes, until the edges are deeply golden, the base looks crisp and the cheese is bubbling in small bronzed patches.
8. Leave the tart to rest for 5 minutes. Finish with a few thyme leaves and more black pepper, then cut into four generous pieces. Serve warm with a simply dressed green salad, if you like.

• Make ahead:Cook the mushrooms up to one day ahead; chill once completely cool.
• Keep:Refrigerate airtight for up to 2 days. Reheat on a hot tray at 190°C / 170°C fan for 8-10 minutes.
• Allergens:Contains gluten, milk, egg and mustard.

• ♡ Cook the mushrooms up to one day ahead.
• ♡ Best on the day it is baked.
• ♡ Reheat on a hot tray, never in the microwave.

Written by Esther

Esther is a photographer and storyteller, and the founder of Essy's Essentials - a seasonal home for stories, rituals, recipes and everyday luxuries.

Published 30 August 2026 · Updated 3 August 2026

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