I am having guests for brunch and want to make larger quantities of  my favorite strata.  Can I just multiply all of the ingredients by four and follow the instructions?

-- Andrea

Generally, it is possible to double (or half) a recipe just by multiplying or dividing by two, provided you follow some basic rules.  Beyond that, it is usually safer to make batches rather then try to scale a recipe by larger amounts.   To scale any recipe, multiply each of the ingredients by the same factor, 2 to double it.  For seasonings and spices, particularly the stronger flavored ones, reduce the amount that you use to start.

For example, if the recipe calls for a teaspoon of salt and you are doubling the yield, only start with one and a half teaspoons of salt in the doubled recipe.  Where you can safely taste the dish as it is being prepared, you can always go back and add more salt as you cook, if needed.  If not, guests may be able to add more slat at the table.  The perversity of of salt, or more likely the human taste buds, is that if you just double the amount the food will likely end up tasting over-salted. As I said, be conservative with other flavors, too.

If you are halving a recipe, you still should under estimate the amount on flavorings and then increase them as necessary.

For baked foods, like a strata, you can't just use the same size pan and increase the time.  Because the food is thicker there is more chance that the outside will become drier than usual before the inside is cooked.  It is almost always better to use a pan that has double the surface area, or two pans that have are the same size as called for in the original recipe rather than cooking in a deeper dish.  That way, the depth and therefore the cooking time should remain about the same. 

If the recipe calls for an 11" X 7" pan, for instance, then it has an area of about 77 square inches.  Doubling that gives 154 square inches.  A 14" X 10  1/2" pan is pretty close to the right size, then, at 147 square inches.

Still, it is best to check the recipe for instructions on how to tell if the food is cooked.  Some recipes may specify and internal temperature, others a toothpick test like baking a cake.  Whatever the instructions follow them.  Also, be sure as you are cooking the dish to turn pans, swap them left to right or front to back or even between shelves, to reduce the effects of any unevenness in your oven temperature.

For roasts, the time to cook is approximately a direct multiple of the weight, although not exactly.  It is always best to use a thermometer to check the internal temperature, rather than rely on time alone to guide cooking.

Recipes like stews will take longer to get up to cooking temperature, but once there the cooking time will be approximately the same as the original recipe.   Be careful, however, to maintain adequate heat.  Larger pots take more heat to stay at the same temperature, which may not be possible to achieve on a home range.  Larger pots also lose heat over a larger surface area so the top of a stew prepared on the cooktop may be noticeably cooler than the liquid below.