Tip the flour into a large bowl. Add the yeast to one side and the sugar and 2 tsp salt to the other. Mix gently. Add 300ml warm water and the melted butter. Mix into a soft dough.

Tip the dough out onto a clean work surface and knead for 5 mins until soft and springy. Return to the bowl, cover with a tea towel and leave to rise in a warm place for 1 hr.

Divide the dough into 15 equal pieces, then roll each piece into a 45-50cm-long rope. Working with one rope at a time, lay the rope in a U-shape with the curved end facing you. Cross the two ends over each other, then lift them up and press down into the curve of the U-shape. Arrange the pretzels on an oiled baking tray and loosely cover, then leave to rise for 30 mins.

Bring 2-3 litres water to the boil in a large pan and tip in the bicarb. Carefully lower in each pretzel and boil for 30 seconds, then gently turn over using a slotted spoon or fish slice. Boil for another 30 seconds. (You’ll need to do this in batches.) Arrange the pretzels on baking trays lined with baking parchment. Heat the oven to 200C/180C fan/gas 6. Sprinkle sea salt flakes over the pretzels, then bake for 15-20 mins until golden brown.

Meanwhile, make the dip. Melt the butter in a medium pan over a medium heat and, once foaming, stir in the flour to make a paste. Cook for 1-2 mins, then slowly pour in the milk, whisking continuously until smooth. Bubble for 1-2 mins.

Remove from the heat and stir in the cheeses until the mixture is smooth and thick – return to the heat for 1-2 mins if the cheeses don’t melt fully. Stir in the mustard and paprika. Season. Once cooled, will keep chilled with baking parchment over the surface, for a day. Reheat over a low heat with a splash of milk until piping hot. Serve immediately with the pretzels.