The soft pretzels and pretzel buns that you see in commercial bakeries are boiled in water with added “pretzel lye”. This is an alkaline addition that is key to the colour and texture of pretzels, but is highly caustic and not recommended for home use. Using baking soda in the boiling liquid creates an appropriate and most importantly, safe alkaline liquid for the pretzels– the texture is virtually the same, although the colour will be a slightly lighter brown.
Stir the water, milk, melted butter, yeast and sugar together. Add the flour and salt and stir until the mixture becomes too dense to do so (and it is a dense dough), then turn it out onto a lightly floured surface and knead the dough by hand until it feels elastic and smooth, about 5 minutes. Return this to the mixing bowl, cover the bowl with plastic wrap and set aside to rise for 90 minutes.
Turn the dough out onto your work surface and divide it into 12 equal pieces. Using as little flour as possible, roll each piece of dough into a length of ‘rope’ about 12-inches (30 cm) long. Drop the rope onto the table as an elongated “U”, then twist the dough around twice and place the ends over the bottom curve of the “U” to create the signature pretzel shape. Once you are happy with the shape, press the ends gently down to secure and lift the pretzel onto a parchment-lined baking tray (make sure the tray is coated, not aluminum). Once all assembled, cover the pretzels with a tea towel to rise again for 20 minutes.
Preheat the oven to 350 °F (180 °C). Fill a stainless steel 4 L pot with 1 L of water and bring it to a full rolling boil. Add the baking soda (the water will foam briefly) and then carefully drop in 2 to 3 pretzels into the water. Boil the pretzels for 90 seconds without turning. Lift them out with a slotted spoon back onto the baking tray. Repeat with the remaining pretzels, in batches.
Brush the boiled pretzels with the egg wash and sprinkle with coarse salt. Bake the pretzels for 20-25 minutes, until they are an even rich brown.
Soft pretzels are best enjoyed within 5 hours of being made.