2 8.5-oz. pkgs. Jiffy Cornbread Mix
1 cup freshly grated Parmesan cheese, divided
2 teaspoons ground black pepper
2 teaspoons chopped fresh thyme
¼ cup cold unsalted butter, cubed
3 large eggs, divided
¼ cup cold whole buttermilk
Preheat oven to 350°F. Line a baking sheet with parchment paper or use a Silpat.
In the work bowl of a food processor, place cornbread mix, ¾ cup cheese, pepper, and thyme; process until combined. Add cold butter, and pulse 5 to 6 times until mixture is crumbly.
In a small bowl, whisk together 2 eggs and cold buttermilk. With processor running, add egg mixture in a slow, steady stream just until moistened. (Batter will be thick.)
Using lightly greased hands, spread dough into a 12” x 4” rectangle on prepared pan. In a small bowl, beat remaining egg, and brush over dough. Sprinkle with remaining ¼ cup cheese.
Bake until lightly golden and firm, about 20 minutes. Let cool for 10 minutes. Reduce oven to 300°. Using a serrated knife, cut crosswise into ½-inch-thick slices. Place slices cut side down on pan. Bake until golden and crisp, 15 to 20 minutes more. Let cool completely. Store in an airtight container for up to 1 week.