Measure the flour, salt, sugar and yeast into the bowl of an electric stand mixer, fitted with a dough hook. 

Lightly mix the ingredients together.

With the speed on low, slowly add the warmed milk.

Keep mixing on low speed until the ingredients come together into a sticky dough.

Add the butter, about a tablespoon at a time, waiting for it to be completely incorporated before adding the next tablespoon.

Once all of the dough ingredients have been added, mix the dough on a low-medium speed for about 15-20 minutes, or until you have a soft and smooth ball of dough. When you poke the dough gently, it should bounce back immediately.

Lightly oil a large bowl.

Place the dough into the bowl, and cover with some plastic wrap or a reusable bowl cover.

Leave the dough somewhere warm for 1 to 1.5 hours, or until the dough has doubled in size (see Kitchen Notes below).

During this time, start baking the baking soda (see instructions below for the baking soda bath).

Once the dough has doubled in size, punch back the dough to release all of the air.

Knead the dough gently a few times.

Weigh the dough and divide this number by 10 to get the weight for each bun. 

Divide the dough into 10 equal portions. Alternatively, if you wish to make smaller pretzels, divide the dough into 12 pieces.

Line a large baking tray with baking paper.

Roll each piece of dough into a smooth ball, and then roll each ball into a log measuring about 60 cm/24 inches.

Form each log into a U shape.

Cross over the ends to form a loop.

Cross over the ends once again.

Bring the ends down over the loop to form the pretzel shape.

Place the pretzels onto the lined baking tray.

Repeat the above steps until all of the pretzels have been formed.

Place the tray of pretzels somewhere warm for about 30 minutes to puff up slightly.

Preheat the oven to 120°C/250°F (without fan).

Place the baking soda in an oven-proof dish which is large enough to hold the water later.

Bake the baking soda for 1 hour.

Remove the dish from the oven and let the baking soda cool completely.

When you are ready to prepare the pretzels in the next step below, make the baking soda bath (or lye water) by dissolving the water in the baked baking soda. Whisk until everything is dissolved. Sometimes, there are lumps of baking soda which remain, which is fine but make sure these do not stick to the dough later.

Carefully place a pretzel dough into the baking soda bath using a large metal spider or slotted spoon. As the baking soda bath can irritate the skin, wear some gloves and/or avoid touching the water with your bare hands.

Submerge the pretzel dough in the baking soda bath for 5-10 seconds.

Lift the pretzel dough out of the water, and drain off as much water as possible.

Transfer the pretzel dough from the baking soda bath back to the lined baking tray.

Try to handle the pretzel dough carefully and to not deflate them. However, don't worry if they look soggy after their water bath.

Repeat the above steps with the remaining pretzel dough.

Preheat the oven to 200°C/390°F (without fan).

Sprinkle the pretzels with sea salt and/or your choice of topping.

Bake the pretzels for 15-20 minutes, or until they are golden and cooked through.

Brush the warm pretzels with some milk to keep them glossy.

Serve warm.