Hi Anne, I think trying to scale up such a small recipe will be fraught with difficulty. Far better to start with a proven bulk recipe. Use the forum search feature with "bulk" in the search box and "search only in titles" ticked. This will show up a few, but all will rely on the use of a separate base, so refer to the base gravy section of the forum for those. Most will use around 3kg onions and make around 15 or 20 portions so you may have to scale up these, but at least you're working with multiples of 2 or 3 rather than 25.