OK, this is from Barbara Lord’s Green Cleaner – can’t vouch for it personally.
You will need:
1 cup water
Half a cup cloudy ammonia
Mix water and ammonia in an oven proof dish or bowl. Place the dish in warm oven 10-15 minutes or longer if the oven is really dirty. It can be left overnight and cleaned the following day. Wipe off burnt on grime with scourer and bicarb soda.Wipe over with a clean damp cloth. Repeat if badly stained.
After the cloudy ammonia treatment, shelves and glass will also come clean with a scourer and bicarb soda.
I use an old baking dish that has outlived its cooking days. Keep it in the laundry cupboard with cleaning equipment so it isn’t used for cooking.
If you suffer from asthma, wear a surgical mask when cleaning with ammonia as the fumes may be damaging to people with nose, throat or chest problems.
The outside of the oven and around the hotplates only needs bicarb soda on a damp cloth, even where cooking spills have hardened. Burnt on grime may need to have a paste of bicarb soda left on it for a while.
Line the bottom of the oven with easily replaced aluminium foil so it catches the spills, or leave an old tray in the bottom of the oven for the same purpose.