Things to know:
A frying pan with an expand enchant is necessary to make large meals.
Currently the quality of the julbord has no effect on its function. Xype (the admin) had wanted to make a mod that makes the julbord take quality into account, in that the quality would determine how many times a julbord can be eaten from, then it would need to be replenished with meals. There is no news on if/when this mod will be written. It is unnecessary at this time to worry about quality.
The crafting recipe requires .7kg or greater meal size per crafting action (adding 1 meal to unfinished julbord). This means that 35kg total kg of meal(s) are needed to craft a julbord.
If you divide 35kg by .7kg you would need 50 (.7kg) meals to craft a julbord. However, you can make larger meals than .7kg and save yourself some cooking time.
A meal's kg is equal to the sum of its ingredients kg.
Use a basic meal recipe of 1 meat and a large number of vegetables to create a large meal in an expanded frying pan. Naturally, you would want to use a vegetable with a high kg to maximize meal size.
Therefore, 70 tomatoes + 1 meat = 35.3kg meal, perfect for making a julbord.
A frying pan with a 57 expand cast can hold 70 tomatoes and 1 meat to make a 35.3kg meal. A frying pan with a 75 expand cast will hold 99 tomatoes and 1 meat and make a 49.8kg meal.
From here you should be able to come up with your own method of making julbords in the most efficient manner possible.
NOTE: The quality of your meals affect the chance of adding them to the unfinished julbord. Crafting failures add damage to your meals. Low quality meals may be destroyed by damage before you can add them to the julbord. This is why high quality ingredients and hot food cooking skill are important. Of course, to get high quality ingredients you need to have farming skill (vegetables) and butchering skill (meat) along with high quality tools for those skills. You can get by with low skill and low quality ingredients, you'll just be cooking more meals.