Preheat oven to 200°C (400°F). Toss mushrooms with olive oil and spread across a baking tray. Season well and roast in oven for 10 minutes. Allow to cool.

To make the hot water pastry, bring butter and water to the boil in a medium saucepan over a high heat. Remove from the heat, add the flour and salt and mix well. Tip pastry onto a worktop and knead to bring it all together – still warm, it feels deliciously smooth and silky – then roll it out on a large sheet of greaseproof paper into a rough circle, until approximately 30cm across.

Spread carmelised onions in the centre of the pastry, leaving a 2cm border. Sprinkle with goat cheese, asparagus and roasted mushrooms, along with any juices. Drizzle with a little olive oil, then sprinkle with thyme. Fold the edges of the pastry over the filling, brush the pastry with beaten egg and season with sea salt and fresh ground pepper.

Bake for 30-35 minutes, or until the pastry is crisp and the fillling bubbling.

https://bibliocook.com/2021/06/spelt-pastry-galette-with-mushrooms-asparagus-goat-cheese/