1. Heat: Turn your kitchen oven on to 200°F. Allow the appliance to heat for 15 minutes, then turn off the oven completely and keep the door tightly closed to contain the warm air inside.

2. Pour: Measure and pour 1/2 cup of ammonia into a shallow baking pan. Place this pan carefully onto the top shelf of the warm oven.

3. Steam: Pour 2 cups of boiling water into another separate shallow pan. Place this pan immediately onto the bottom shelf of the oven.

4. Sit: Close the oven door completely and leave both pans inside undisturbed for at least 2 hours, or for much better results, leave them sitting overnight.

5. Remove: Take both pans out of the oven carefully after the sitting period is over, and dispose of the leftover liquids safely down your drain.

6. Mix: Combine the remaining 1/2 cup of ammonia, 1/2 cup of baking soda, and 1 cup of white vinegar together in a small mixing bowl to form a thick cleaning paste.

7. Spread: Put on heavy rubber gloves to protect your hands, then spread the freshly made baking soda paste evenly over the interior oven surfaces using a heavy cloth or rag.

8. Wait: Allow the applied cleaning paste to sit undisturbed on the interior oven surfaces for about 15 minutes to loosen the grease.

9. Scrub: Use a scrubbing sponge or durable steel wool to vigorously scrub away the baked-on grease inside the oven's interior.

10. Wipe: Clean all the internal surfaces thoroughly with a fresh damp cloth to completely remove any leftover baking soda paste.

11. Repeat: Apply additional coats of the fresh cleaning paste over any persistent, stubborn dark spots as necessary until the metal is completely clean.

12. Shine: Enjoy the beautiful, grease-free sparkle of your clean oven.