In a large bowl, mix warm water, yeast, and brown sugar. Let it sit for about 5 minutes, or until it becomes frothy.

Stir in flour and salt until combined. Knead the dough on a floured surface for about 5-7 minutes, until smooth and elastic.

Place the dough in a greased bowl, cover it with a damp towel, and let it rise for about 1 hour, or until the dough doubles in size.

While the dough is rising, preheat your oven to 450°F (232°C) and line a baking sheet with parchment paper.

Once the dough is ready, bring a large pot of water to a rolling boil and stir in the baking soda.

Divide the dough into 12 equal pieces. Roll each piece into a long rope, then twist into a pretzel shape. Tuck a mozzarella cube into the center of each pretzel and seal well.

Carefully place the pretzels in the boiling water, one at a time, for about 30 seconds. Remove and place them on the prepared baking sheet.

Brush with egg wash and sprinkle with sea salt.

Bake for 12-15 minutes, until golden brown. Let them cool slightly before serving.