Preparation (10 minutes)

1. Preheat oven to 425°F (220°C) with rack in lower third position. Place empty metal pan on oven floor for steam generation.
2. Line loaf pan with parchment paper, leaving overhang for easy removal. Lightly grease parchment.
3. Bring ingredients to room temperature (70-75°F): Set eggs and buttermilk out 30 minutes before baking, or quick-warm buttermilk in microwave for 20-30 seconds.

Flour Blend Preparation (5 minutes)

4. Sift dry ingredients together twice through fine-mesh strainer: white rice flour, brown rice flour, potato starch, tapioca starch, salt, and optional seasonings.
5. Add xanthan gum and whisk vigorously for 30 seconds to eliminate clumps.
6. Create well in center of flour mixture and set aside.

The Cheese Pocket Method (10 minutes)

7. Prepare cheese coating: Toss both grated cheeses with 2 tablespoons flour blend until evenly coated.
8. Let cheese stand 10 minutes at room temperature – this prevents clumping and improves melting behavior.

Chemical Leavening Assembly (5 minutes)

9. Add leavening agents to flour mixture: baking soda, baking powder, and cream of tartar. Whisk to distribute evenly.
10. Combine wet ingredients: In separate bowl, whisk together buttermilk, eggs, and melted butter until smooth.
11. Add vinegar to wet ingredients just before mixing – this activates baking soda immediately.

Final Assembly (3 minutes)

12. Pour wet into dry: Add wet mixture to flour well and gently fold until just combined – no more than 15 strokes. Batter should look slightly lumpy.
13. Add prepared cheese: Fold cheese into batter with exactly 8 gentle strokes for optimal distribution.

Baking Protocol (35-40 minutes)

14. Transfer to pan and smooth top gently. Place in preheated oven.
15. Create steam: Immediately add ½ cup hot water to metal pan on oven floor.
16. Initial bake: 15 minutes at 425°F without opening oven door.
17. Reduce temperature to 375°F, tent with foil, and continue baking 20-25 minutes.
18. Check doneness: Internal temperature should reach exactly 205°F on instant-read thermometer.

Cooling Process (1 hour)

19. Cool in pan 10 minutes on wire rack to set structure.
20. Remove from pan using parchment overhang and cool completely before slicing (approximately 1 hour).

Critical Success Tips:

• Don’t overmix – lumpy batter is correct
• Use instant-read thermometer for accuracy
• Cool completely before slicing to prevent gummy texture