In a large jug mix together the yeast, warm water and honey until combined then set aside for 5 - 10 minutes until frothy and bubbled up.
In the bowl of a stand mixer fitted with a dough hook add the plain flour, wholemeal flour and salt and mix to combine. Slowly add the yeast mixture, mixing on low speed until everything is incorporated. Increase the speed slightly and knead together for 5 - 8 minutes, until the dough is smooth and comes away from the sides of the bowl easily. Transfer to a lightly greased bowl and cover with cling film then place in a draft-free place for about 1 hour, or until doubled in size.
Preheat oven to 230 C / 210 C fan and grease and line 2 large baking trays.
Place the water and bicarbonate of soda in a deep saucepan and set over a high heat to come to a boil.
Remove the dough from the bowl and divide into 16 pieces. Roll each piece into a rope about 23 - 25cm long. Continue until all the pretzels are rolled.
Once the water is boiling, drop the pretzels in, one at a time, and boil for about 20 seconds. Remove with a slotted spoon and place onto the prepared baking sheets, bending them into staff shapes as you place them down. Once all the pretzels have been boiled, brush them with the egg wash and place them in the oven to bake for about 8 - 10 minutes.
Remove from oven, brush tops with melted butter and sprinkle with salt then serve warm with the mustard.