1. Start by making the pretzel dough. Combine milk, water, honey and sugar in a microwave safe bowl, and microwave on high for 30 seconds.
2. Pour the mixture into the bowl of a stand mixer, and add the yeast, then leave it to bloom 10-15 minutes.
3. Add both flours and melted butter to the mixture, and using a dough hook attachment, mix 5-7 minutes until the dough comes together in a large ball.
4. Place the dough on a floured board or silicon matt, and divide into 12-14 even pieces, then cover with a damp dish cloth and allow to proof, 15 minutes.
5. Roll each ball out into a disc, and spread in a single layer on the matt, then cover again with damp towel to proof a further 30 minutes.
6. In a skillet over medium heat, cook the chorizo, breaking it up into small pieces with a spoon as it cooks. Remove from heat once cooked through.
7. Preheat an oven to 425 degrees, place a large pot of water on the stove to boil and line a baking sheet with parchment paper.
8. After the proofing time is done, place a single disc on a board, spoon a tablespoon of chorizo into the middle of the disc, then top with a generous pinch of mozzarella. Gather the sides of the disc at the tip and pinch them together, making sure they are sealed well. Place the formed bun on the tray and cover with another damp cloth.
9. If the dough discs seem to be getting dry, you can spritz them with a light mist of water. Repeat the stuffing until all the buns have been created.
10. Making sure the pot of water it at a rolling boil, dump in the baking soda, then drop 3-5 buns in to cook 15 seconds per side. Work only a few buns at a time, to avoid overcrowding the pot. Once boiled, remove the bun using a mesh strainer and place back onto the tray. Repeat until all buns have been boiled.
11. Place the tray immediately into the oven, and cook buns 15-20 minutes until they are a dark brown color. They are best eaten while still warm.