In a large bowl, combine the warm water, brown sugar, and yeast. Stir gently to combine and let it sit for about 5-10 minutes until it becomes foamy. This indicates the yeast is active.

Add the ground mustard powder, flour, and salt to the yeast mixture. Incorporate the flour gradually. Using a spoon or spatula, mix until no dry flour remains. The dough will be sticky; this is okay!

Cover the bowl with a damp cloth or plastic wrap. Set it in a warm, draft-free place. Allow it to rise for at least 1 hour or until doubled in size.

Once the dough has risen, flour your work surface. Gently turn the dough out and divide it into 8-10 equal portions. Shape each piece into a roll, tucking the edges underneath for a round shape.

In a large pot, bring the water to a gentle boil. Gradually add the baking soda. Be careful, as it can bubble up! Once it’s dissolved, reduce it to a simmer.

Carefully drop a few rolls into the water bath. Boil each one for about 30 seconds, flipping halfway through. Remove with a slotted spoon and place them on a baking sheet lined with parchment paper.

While the rolls are still wet, you can brush them with melted butter and sprinkle with coarse sea salt if desired.

Preheat your oven to 425°F (220°C). Bake the rolls for 15-20 minutes or until they are golden brown.