In a large mixing bowl, whisk together your room-temperature sourdough discard, warm water, and instant yeast until combined. Let the mixture sit for about 10 minutes, or until it becomes bubbly and fragrant.

Add the all-purpose flour, salt, and sugar to the bubbly yeast mixture, stirring with a wooden spoon until a shaggy dough begins to form.

Transfer the dough onto a lightly floured surface and knead it for about 10 minutes until it's smooth and elastic.

Place the kneaded dough into a lightly greased bowl, cover it with a clean kitchen towel, and let it rise for about 1 hour, until it has doubled in size.

While the dough rises, prepare the garlic butter. Melt unsalted butter in a small saucepan, then stir in minced garlic and chopped parsley. Allow it to simmer for about 2-3 minutes until fragrant.

After the dough has risen, roll it into a rectangular shape, brush it generously with garlic butter, and sprinkle the shredded mozzarella cheese over the top. Cut the dough into squares and stack them vertically in a greased baking pan.

Cover the assembled dough in the pan and let it rest for another 30 minutes. Preheat your oven to 350°F (175°C).

Once the dough has puffed up, bake for 30-35 minutes until golden brown and sounds hollow when tapped.

Let cool in the pan for about 10 minutes, then pull apart the fluffy pieces and slice as desired.