
Over the next 30 minutes, slowly heat the curds to 100☏, stirring frequently. Using the knife, carefully cut the curds into ¼-inch cubes and allow to set for 5 minutes. You should see a layer of mostly clear whey floating on top of the curd, and the curd should be pulling away from the sides of the pot. Remove from heat source and allow the cheese to set for 1 hour, or until the whey begins to separate from the curd. Using an up-and-down motion with your spoon will ensure that the rennet works its way through all the milk, so you can get the highest possible yield. Stir to homogenize the milk, and slowly fold in the diluted rennet.
If it naturally drops in temperature, that is OK.)
When the milk gets to 85☏, add culture, stir in with an up-and-down motion, cover, and ferment for 1 hour. As the milk is heating, add the calcium chloride, if using. In a large pot, heat the milk to 85☏, stirring frequently. To recrisp after refrigerating and serve warm, heat in a 350 degree oven for 5 minutes. Store cookies in an airtight container at room temperature overnight, then refrigerate for up to 1 week. Let cookies cool on the baking sheets for 2 minutes, then transfer them onto wire racks to cool completely. Bake, switching the sheets from top to bottom and rotating halfway through, until golden and just firm (they will continue to crisp up as they cool), 23 to 25 minutes. Arrange them on the prepared sheets about ½ inch apart. Using a sharp knife, slice chilled logs into ¼-inch-thick slices. Line 2 baking sheets with parchment paper or aluminum foil. Place racks in upper and lower thirds of the oven and heat oven to 350 degrees. Wrap each piece of dough in plastic wrap and chill until firm, about 2 hours or overnight. If using sesame seeds, spread them onto the work surface and roll the log over the seeds until lightly coated. Roll each half into a log that is 1 inch in diameter and about 12 inches long. Transfer dough to a lightly floured work surface and divide in half. Continue pulsing and drizzle in 2 tablespoons of ice-cold water just until the dough comes together.
Add butter and scallions, and pulse just until well blended, about 30 seconds.
In the bowl of a food processor, combine flour, both cheeses, black pepper, salt and paprika, and pulse until well combined and sandy, about 30 seconds.