1. Pulse both flours, sugar, and 2 teaspoons salt in a food processor to combine. Add butter and pulse just until small pieces remain. Add 6 tablespoons ice water and pulse until dough just starts to clump together. Add more water, 1 tablespoon at a time, if necessary.

2. Turn dough out onto a clean work surface; divide in half. Wrap each half in plastic and press to form a flat rectangle. Refrigerate until firm, at least 1 hour and up to 1 day, or freeze up to 1 month.

3. On a lightly floured piece of parchment, roll out each piece of dough into a 10-by-14-inch rectangle. Refrigerate until firm, about 30 minutes.

4. Meanwhile, whisk together 6 eggs, milk, 1/4 teaspoon salt, and 1/8 teaspoon pepper. Heat a large nonstick skillet over medium-high. Add sausage and cook, turning occasionally and breaking into small pieces with a wooden spoon, until browned, about 8 minutes. Using a slotted spoon, transfer to a bowl. Remove all but 1 tablespoon fat from pan, reduce heat to medium, and add egg mixture. Cook, stirring, until eggs are soft and just set, 2 to 3 minutes. Remove from heat, sprinkle with cheese and chives, and stir in sausage. Let cool slightly.

5. Preheat oven to 425 degrees with racks in upper and lower thirds. Transfer one rectangle of dough on parchment to a baking sheet. Arrange filling into nine 2 1/2-by-3 1/2-inch rectangles on dough (in a 3-by-3 grid), leaving a 1-inch border all around. Whisk remaining egg; brush borders between filling with egg wash. Top with remaining rectangle of dough. Using the sides of your hands, gently press dough to seal egg-wash grid. Using a pizza cutter, cut into 9 rectangles.

6. Divide pockets between 2 parchment-lined baking sheets. Use a fork to score edges of each pastry. Brush tops with egg wash, then dock a few vents in top crusts with fork. Season with pepper. Refrigerate until firm, 15 minutes.

7. Bake, rotating sheets once, until golden brown, about 30 minutes. Let cool slightly before serving.