In a large mixing bowl, combine the warm water, sugar, and yeast. Let it sit for 5-10 minutes, or until it becomes foamy.
Add the flour, ¼ cup melted butter, and salt to the yeast mixture. Stir until a dough forms.
Knead the dough on a floured surface for about 5 minutes, or until it is smooth and elastic.
Place the dough in a greased bowl, cover it with a clean kitchen towel, and let it rise in a warm place for 1 hour, or until it has doubled in size.
Preheat your oven to 450°F (230°C). Line a baking sheet with parchment paper.
In a large pot, bring the 10 cups of water and baking soda to a boil.
Divide the dough into 16 equal pieces. Flatten each piece into a rectangle, place a piece of mozzarella cheese in the center, fold the dough over the cheese, and seal the edges, forming a ball.
Drop each stuffed dough ball into the boiling water mixture for 30 seconds.
Using a slotted spoon, transfer the pretzels to the prepared baking sheet. Sprinkle with coarse sea salt. Bake in the preheated oven for 12-15 minutes, or until golden brown.
Remove from the oven and brush with the remaining ¼ cup melted butter. Serve warm with marinara sauce for dipping, if desired.
