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1
First, you must bake the baking soda. This step should be done while the pretzels are undergoing their first rise, if not earlier.
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2
Preheat the oven to 250u00b0F/120u00b0C/ gas 1/2. Spread out baking soda on an aluminum pie pan or a small rimmed baking sheet covered with aluminum foil. Bake the baking soda for 1 hour. The baking soda will lose weight as it bakes but maintains about the same volume, so you should end up with about 1/4 cup (60g) of baked baking soda. Allow it to cool completely, and then keep it in an airtight container at room temperature until you are ready to make pretzels. (If you see more than one batch of pretzels in your future, consider baking a whole box of baking soda in one shot, since it keeps indefinitely. Sift baked baking soda before using, as it cakes after prolonged storage.)
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3
Select a large stainless-steel pot and fill it with 8 cups (2L) of water. Be sure to choose a pot that is at least a finger's length wider than the diameter of the pretzels and tall enough so that the water comes up no more than 2 in (5cm) from the rim. (Avoid other metal surfaces, such as aluminum and copper, and nonstick surfaces, which may react with the baked baking soda.) Pour in the 1/4 cup (60g) of baked baking soda, and bring the liquid to a simmer over medium-high heat. Once the baking soda dissolves, reduce the heat to medium to maintain a gentle simmer.
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4
Before baking, brush the tops of the pretzels lightly with an egg wash of 1 egg yolk, beaten with 1 tbsp of water. This will give them a glossy finish.
