In a large bowl, whisk together the flour and salt.
In another bowl, whisk together the milk and yeast.
Make a well in the flour and add the liquid ingredients.
Stir this together until a dough starts to form, then add the butter and knead on a flat surface for about 10 minutes, or until smooth and elastic.
Alternatively, mix for about 8 minutes in a stand mixer with a dough hook.
Cover and let rise for about an hour or until the dough has doubled in size.
Preheat oven to 200°C/400°F/gas mark 6.
Split the dough into 12 pieces, about 70–75 g (2½ oz) each, then roll into buns.
Meanwhile, boil the water in a large pot and add the baking soda.
Gently drop the buns into the boiling water (as many as fit comfortably in the pot, usually around 3-4) and count slowly to ten.
Use a slotted spoon or sieve to remove the buns, shake off excess water and place them on a cooling rack on a parchment-lined baking sheet.
Once they have all been dipped, slice the tops with a sharp knife (preferably serrated) and then bake for about 20 minutes, or until they are a deep brown on the top and bottom.
