In a medium bowl, stir together cream cheese, garlic powder, black pepper, salt, and red pepper (if using) until smooth; stir in mozzarella and Parmesan. Fold in spinach and artichokes. Cover and refrigerate until ready to use.

Cut 12 (6x5¼-inch) rectangles of parchment paper. Place rectangles on rimmed baking sheets; dust with flour.

On a clean surface, divide Pretzel Dough into 12 portions (about 75 grams each). Gently deflate 1 portion of dough to release any large air bubbles, and shape into a round. (Keep remaining dough covered to prevent it from drying out.) Place on a prepared parchment rectangle. Repeat with remaining dough. Cover and let rise in a warm, draft-free place (75°F/24°C) until puffed, 30 to 45 minutes.

Preheat oven to 375°F (190°C).

In a medium saucepan, bring 8 cups (1,920 grams) water and baking soda to a low boil over medium-low heat.

Using parchment to transfer, carefully lower buns, 1 or 2 at a time, top side down, into boiling water-baking soda mixture; discard parchment. Cook for 30 seconds per side. Remove dough using a large slotted spatula or spoon, letting excess water drip off; place 1 inch apart on nonstick baking sheets.

Gently press down center of each bun. Spoon about 1½ tablespoons (32 grams) filling into each indentation. Sprinkle coarse salt and sesame seeds onto buns.

Bake, one pan at a time, until golden brown, 12 to 16 minutes. Let cool on pans for 5 minutes. Serve warm or at room temperature. Refrigerate in an airtight container for up to 3 days.