Upsizing recipes for the holidays

[BadRabbit]

We are doing a very large Thanksgiving this year with my extended family + my brother's in laws. Everyone is making a couple of dishes.

Given the size of the crowd (around 25 as compared to our usual 12), what are the tricks to enlarging the recipes?

Specifically, I'm making potatos gratin and will need to make at least double my usual amount. I have a VERY large gratin dish but I am wondering what doubling will do to my bake time (it usually cooks for 45 minute at 375 and I use about 2#s of potatos).

I'm also wondering if I should just cook two Pyrex dishes with a recipe per (same oven) instead of using one big dish.

Is there a general formula for how additional mass will effect cook time? Is it just related to overall mass in the oven or does it have to do with how thick\deep the ingredients are in the pan?

Any other tips to doubling\trebling recipes?

Edited November 14, 2011 by BadRabbit (log)

[Lisa Shock]

If the thickness, depth, is the same, you do not need to increase cooking time by much. I'd add ten minutes for your gratin. Make sure your oven is pre-heated. Yes, the additional mass will initially cool the oven a bit more than a single batch, but, overall, thickness is the real issue.

Most issues involve bringing a larger mass up to temperature. Like, a 4 gallon pot of water to boil potatoes will come a boil much more slowly than a 3 quart pot. Once the potatoes are in and the whole pot has rebounded and is boiling, the potatoes themselves take the same time to cook no matter what.

I'd invest in a couple of probe thermometers (available at places like Target for under $25) and use them to keep tabs on what's happening.

[BadRabbit]

I have some temp probes but I usually only use them for meat.

I kind of figured that thickness would be the deciding factor. I don't imagine thickness/time is linear either.

I know that Doug Baldwin has done a chart with meat thicknesses but is there something similar somewhere for veggies? Or are the thermal properties close enough that I could at least get an idea of timing?

[janeer]

I have a very large family and our "usual" is 20-35 people. My personal preference is to divide into two dishes, not so much for cooking time (equal depth is equal time,for the most part, with a bit more thrown in), but because I can put one dish on either side of the table (or on two tables, as is sometimes needed); also, it's possible for some rich dishes to keep one in the oven, staying warm, to be brought out for seconds when needed (I sometimes stagger the cooking times, putting the second dish in later). And sometimes you end up with one untouched dish, instead of two half-eaten dishes, that can be put in the freezer or fridge for a few days or brought to the neighbor's next day. Of course, you need lots of dishes for this; I have accumulated them of necessity.