How to clean Convection Oven

Gather the following "oven cleaning ingredients: household ammonia, baking soda, white vinegar, 2 overproof shallow glass bowls, sponge, rubber gloves and some boiling water.
Preheat oven at 200 degree Celsius for 15 minutes.
Line one glass bowl with approximately 1 inch of ammonia. Place it on the top shelf of the oven on a wire rack.
In the other glass bowl, pour about 1 inch of boiling water. Place this on the bottom shelf.
Close the oven door and leave it for at least 2 hours; leave overnight if the oven is heavily soiled.
After 2 hours ( or the next morning ) make the oven-cleaning paste as follows: In a glass bowl, pour 1 teaspoon ammonia, 1tsp baking powder and a capful of white vinegar. Mix thoroughly.
Remove the glass bowls containing ammonia and water from the oven and the wire racks,
Using a damp cloth, wipe out the oven well.
Dampen the sponge and work in the cleaning paste with it. Scrub all the surfaces well - the insides, the glass and even the outside. Most of the grime should be off now.
For particularly stubborn spots, let the paste sit on for a bit before scrubbing. Finish with a swipe of damp cloth.