Position oven rack in bottom third of oven. Preheat oven to 450°F (230°C).

In a large bowl, sift together flour, baking soda, and fine salt. Make a well in center. Add 1½ cups (360 grams) buttermilk. Using one hand like a claw, slowly fold flour mixture from sides of bowl into buttermilk until a softish, slack dough forms, adding up to remaining ¼ cup (60 grams) buttermilk if necessary. Turn out dough onto a lightly floured surface, and knead lightly for a few seconds; shape into a ¼-inch-thick rectangle. Turn dough over, and lightly roll into a 12×8-inch rectangle.

Brush a 13×9-inch baking pan with extra-virgin olive oil. Place dough in prepared pan. Press dough to fill pan, and sprinkle with rosemary. Scatter chorizo evenly onto dough. Spread pizza sauce over chorizo; place bocconcini on top. Sprinkle with Parmesan.

Bake for 15 minutes. Reduce heat to 400°F (200°C), and bake until cheese is browned and bubbly and an instant-read thermometer inserted in crust registers 200°F (93°C), 20 to 25 minutes more. Sprinkle with parsley, green onion, and flaked salt, if desired. Let cool for 5 minutes before serving.