Buffé Veteran requires you to eat 500 pieces of food.
Food can be acquired from fruit trees and bushes, which do not spawn randomly, but have fixed positions. For a good guide on types of fruit trees, check out this guide by Jynn.

However, gathering 500 pieces of food can be a tremendous grind due to the sparse spawn rate of the food. I've managed to find a perfect place to farm fruit and have optimized my strategy to being able to harvest 500 in about 5 days, whilst taking spawn rates into account and about 7.5 hours of total playing time.
Read more in the next section.

Thanks to Nemo for creating this map!

You'll want to go to the lake lying west of the spawning tree. Around the lake are four fruit sources very close to each other - two blue berry bushes, one acorn tree and one red berry bush.

Your strategy will consist on choosing a server and grove and running the route I drew on the map forth and back, picking up all fruit you find on the way.
Once you've reached one end of the trail, go back to the den and switch to the next grove (this method is called grove hopping). If you've run out of groves, close the game and switch to a different server.

One run across all 27 groves will net you somewhere around 100 pieces of food, depending on grove activity and pure luck. One run took me under 1.5 hours.

A vital skill to use when doing these runs is the scent ability, which is triggered with the middle mouse button on normal control settings. This will let you clearly see all fruits on bushes/trees from quite a distance, and let you clearly distinguish unripe fruits from ripe ones.
Here are three images showing the difference between ripe and unripe food on scent mode for the three fruit types that are encountered throughout this run:



Due to the long respawn duration of the fruit, I would not recommend repeating the run more than once a day. I tried repeating it every 12 hours and only got about half the harvest compared to waiting for 24 hours. Given the small amount of achievement hunters playing Meadow, it is unlikely you'll run into somebody grinding at the same place at the same time, so I would highly recommend waiting at least a day between each run.

Thanks for reading my guide. Please post any questions in the comment section; I will try my best to answer them. If my guide has helped you, I'd also be very happy about a rating and a comment.

Thanks go out to Nemo for creating the awesome map and Jynn for his guide on Food in general, which helped me tremendously finding my way around the new content.