WARNING: VERY LONG! But it solves all questions.
tl;dr
4 stacks of 459 Hydra Meat are worth 1982880☼. That beats everything, except the h4x roast. But I still have to say, to get around 2% of its value is pretty impressive. The most expensive SINGLE roast, however, is 4 dragon meat deluxe: 1,560☼ each.
OK... assuming values are done in the same way that 40d did meal values, we have a few options:
Base: Dragon Meat, Whale Meat, or Elephant Meat
Additions: Dragon Meat, Whale Meat, Elephant Meat, dwarven syrup or Sunshine
So, I have a hunch that a stack of 773 * 2 whale meat, and 10 dwarven syrup would be very valuable.
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 1 (whale) * 12 (masterwork) == 24
20 (dwarven syrup) * 12 (masterwork) == 240
20 (dwarven syrup) * 12 (masterwork) == 240
Subtotal (value of one serving): 648☼
648 (value) * 1566 (quantity) == 1014768☼
Alternatively, replacing whales with just a stack of 4 139 Dragon meat would give a value of
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
Subtotal (value of one serving): 1560☼
1560 (value) * 556 (quantity) == 867360☼ (A little bit smaller value, but MUCH easier to get. Killing 4 dragons guarantees this. Now you just need 4 masterwork checks in a row. Hopefully you have your legendary +12 cook!)
Or a hydra!
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
Subtotal (value of one serving): 1080☼
1080 (value) * 1836 (quantity) == 1982880☼ (A winner is HYDRA!)
But this is a little hit and miss, as hydras have a very wide range of food output. If you have some object with a value higher than 600, then the hydra can be higher (3 hydra stacks, and 1 unit of liquid euphoria), but I doubt that strongly. Hydra is the way to go. Maths says so!
BUT WAIT!! Dragons are a good buffer, having a higher value than dwarven syrup, so maybe, with some combo of whales and dragons, we can beat 2 million?? I will try in 8 hours time, after some good dawn's sleep
1 Whale and 3 Hydras are worth
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
2 (meat) * 10 (hydra) * 12 (masterwork) == 240
Subtotal (value of one serving): 864☼
864 (value) * 2150 (quantity) == 1857600☼ [Worsens the value of the meal by ~100k dwarf bucks]
And for my last tricks tonight, 2 whales and 2 dragons:
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
Subtotal (value of one serving): 888☼
888 (value) * 1824 (quantity) == 1619712☼
And 1 whale, and 3 dragons:
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
Subtotal (value of one serving): 888☼
1224 (value) * 1190 (quantity) == 1456560☼
Finally, 3 whales, and 1 dragon
10 (prepared meal) * 12 (masterwork) == 120
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 1 (whale) * 12 (masterwork) == 24
2 (meat) * 15 (dragon) * 12 (masterwork) == 360
Subtotal (value of one serving): 552☼
552 (value) * 2458 (quantity) == 1356816☼