Heat your oven to 170°C.

Cut 240g of your butter into cubes.

Pop your flour and 1 tsp of salt in a large mixing bowl. Add your cubed butter and rub in until the mixture resembles fine breadcrumbs. Add 180ml of cold water and mix thoroughly.

Tip your dough onto your work surface and knead for 5 mins until smooth and elastic. Wrap your pastry in cling film and pop it in the fridge to rest for an hour.

Meanwhile, prep your filling. Peel, halve and slice your onions. Peel your potatoes, then halve and finely slice them.

Heat a sauté pan over a medium heat. Add your remaining butter to the pan and, once melted, tip in your onions and thyme leaves. Fry on a medium heat for 30 mins until really soft and starting to caramelise, deglazing the pan with water occasionally if it looks like they are sticking.

Tip your potatoes into the pan and cook for 5 mins more. Season with salt and very generously with pepper.

Tip your onion and potato mixture into a bowl and, once cool, add your grated cheddar. Stir to combine.

Roll your pastry out to 2mm thickness and use a small bowl to cut out circle shapes about 10cm wide.

Arrange your filling to one side of each circle, then brush the edges with beaten egg and fold over. Seal the edges by pressing down, then twist them inwards to create a braid pattern. Brush the surface with egg wash.

Bake on a parchment-lined baking tray for 40 mins until golden and crisp. Eat hot or cold.