In a large mixing bowl, combine warm water, active dry yeast, and granulated sugar. Let sit for about 5-10 minutes until frothy.

Gradually mix in all-purpose flour and salt, stirring until a shaggy dough forms.

Transfer the dough to a floured surface and knead for about 5-7 minutes until smooth and elastic.

Lightly grease a large bowl, place the kneaded dough inside, cover with a damp cloth, and let rise for approximately 45 minutes.

After rising, punch down the dough gently, divide it into 10 equal pieces, and roll each piece into a 24-inch rope.

Flatten the rope slightly, place a cube of mozzarella in the center, fold the dough over to encase the cheese, and twist ends together to shape into a pretzel.

Arrange shaped pretzels on a parchment-lined baking sheet, cover with a towel, and let rise for another 15 minutes.

In a large pot, bring 10 cups of water to a gentle boil, add baking soda, and dip each pretzel in for 30 seconds.

Preheat oven to 425°F. Place boiled pretzels back on baking sheet, sprinkle with coarse salt, and bake for about 20 minutes until golden brown.

Remove from oven and brush immediately with melted unsalted butter.

Serve warm.