5¼ cups (656 grams) unbleached superfine cake flour3 tablespoons (36 grams) granulated sugar2 tablespoons (30 grams) baking powder1 tablespoon (9 grams) kosher salt2¼ teaspoons (5 grams) roasted garlic powder½ teaspoon baking soda1¾ cups (397 grams) cold unsalted butter, cubed1¾ cups (245 grams) crumbled feta cheese, divided¼ cup (12 grams) chopped fresh chives1¾ cups (420 grams) cold buttermilk⅓ cup (76 grams) unsalted butter, melted
Spray an 8½x4½-inch loaf pan with baking spray with flour. Line pan with foil, letting excess extend over sides of pan.
In a large bowl, whisk together flour, sugar, baking powder, salt, garlic powder, and baking soda. Using a pastry blender or your hands, cut in cold butter until mixture is crumbly. Stir in 1 cup (140 grams) feta and chives. Stir in cold buttermilk until a shaggy dough forms.
Turn out dough onto a lightly floured surface. Pat dough into a rectangle about 1 inch thick, and cut into fourths. Stack fourths on top of each other, and pat into a rectangle. Repeat procedure two more times. Roll dough into a 20×14-inch rectangle (about ¼ inch thick), and cut dough into 20 (4×3½-inch) rectangles. Using a pastry brush, brush melted butter on top of each rectangle; sprinkle with remaining ¾ cup (105 grams) feta.
Stand prepared pan vertically on one short side. Starting at bottom, carefully layer dough pieces (ensuring a 4-inch side is touching bottom of pan), cheese side up, one on top of the other. For final piece of dough, place in pan cheese side down. Turn pan upright onto its bottom. Freeze for 20 to 30 minutes until cold.
Place a piece of foil on bottom rack of oven to catch any dripping butter. Preheat oven to 400°F (200°C).
Bake for 30 minutes; reduce oven temperature to 350°F (180°C), and bake until golden brown and an instant-read thermometer inserted in center registers 205°F (96°C), 1 to 1½ hours more, covering with foil after 40 minutes of baking to prevent excess browning. Let cool in pan for 10 minutes. Using excess foil as handles, remove from pan, and let cool on wire rack for 30 minutes. Serve warm.
PRO-TIP: Lay a sheet of foil on your bottom oven rack. There’s a lot of butter in here, and it might try to make a break for it.