The overnight paste that does the work for you
Mix bicarbonate of soda with enough water to make a spreadable paste, roughly the consistency of thick yoghurt. Add a squeeze of washing-up liquid if you like; it helps the paste cling and cuts grease. Spread it thickly over the interior surfaces — floor, back, sides, the inside of the door — and avoid the heating element, the fan and any visible vents or the oven light. Close the door and leave it overnight, or at least six hours.
In the morning, wipe it off with a damp cloth. The carbon should come away in grey sludge rather than flakes. For anything stubborn, spray the area with a little white vinegar in water: it fizzes against the residual bicarb and loosens the last of it. Rinse several times with clean water, because leftover bicarbonate dries to a white film and will smell when the oven is next heated. Finish by running the oven empty at a low temperature for ten minutes to dry it fully.
Always check your manual first. Some ovens have delicate catalytic liners on the side walls that are designed to burn off grease themselves and must never be scrubbed or pasted. If yours has a pyrolytic self-clean cycle, use it — but remove the shelves unless the manual says otherwise, ventilate the kitchen well, and move pets out of the room while it runs.
