Method

1. Melt the butter in a small saucepan over a medium heat. Once it starts to foam, scatter in the onion and a pinch of salt. Cook for 15-20 mins over a medium-low heat, stirring often, until golden and caramelised. Spread out on a plate and leave to cool completely.

2. Pour the flour, yeast, sugar and 1 tsp salt into the bowl of a stand mixer with the dough hook attached. With the mixer running, pour in 280ml lukewarm water and knead for 5-6 mins, before turning out onto a lightly floured surface. Shape into a ball, then put in an oiled bowl, cover and leave to prove for 1-2 hrs or until doubled in size.

3. Tip onto a lightly floured surface and knock it back. Spread out to a flat rectangle, then scatter over the caramelised onion, re-kneading the dough to distribute. Split into 12 logs. Leave to rest for 5-10 mins.

4. Use your palms to roll out each piece of dough to a rope roughly 35-40cm long. Lay one rope in a U-shape, with the curve pointing towards you, then take the two ends and cross them over twice to make a little twist at the end. Then lift the ends and press them into the curve of the U-shape. Repeat with the rest of the dough, then leave on a tray lined with baking parchment and cover with a clean tea towel to prove for 20 mins.

5. When they have 5 mins left, bring 2.5 litres of water to the boil in a saucepan. Dissolve the bicarbonate of soda in the water. Heat the oven to 200C/180C fan/gas 6.

6. Working in batches, gently lower each pretzel into the boiling water. Cook on each side for 30 seconds, using a slotted spoon or tongs to hold them down, if necessary. Remove to the baking tray, brush each with egg, then sprinkle with some of the gruyère and a little sea salt (flaky sea salt, if you have it).

7. Bake for 20-25 mins until deep golden brown and the cheese is molten and bubbling. Leave to cool for 15 mins before serving. Best served on the day, or will keep frozen for up to a month.