If that can have such a profound effect on taste of a dish coming from the same kitchen and the same cook, I think it is safe to assume that any larger change could have completely palate shatterings effects.
Some time ago, I was in charge of organizing a series of theme parties held at various locations across the country over the course of several years. We had a corps of volunteers to help out, often different people in each place, but we tried to have some consistency in the food served.
One of the things we served were ANZAC biscuits, an Australian cookie. I developed a recipe for American kitchens, tested it out on some Australians and distributed it to our volunteers, who baked at home and brought the finished cookies to the different parties. I tried to make the directions very thorough.
The results we got were wildly inconsistent. As you might imagine, there were differences in size and shape and brownness of the cookies. There were differences based on ingredients: steel-cut oats vs. rolled oats vs. quick oats; U.S. golden syrup vs. British golden syrup vs. corn syrup; butter vs. margarine; etc. The pans used made a difference.
One regular volunteer baker's cookies were so incredibly different from everyone else's that I finally went over to her house to watch her make them. Turned out she'd been throwing everything into her mixer and beating the heck out of it.
After that, I changed the instructions. But the experience was a real lesson in how differently different cooks can make the same recipe turn out.
Another thing that surprised me, given the relatively ordinary ingredients of this recipe, was how different they were across the country. I knew that flour varies across the U.S., even in some national brands; but some bakers weren't able to find old-fashioned oats, and even dark-brown sugar was a problem for some. I didn't even try to tell people to look for unsweetened coconut, which is standard in Australia -- I just adjusted the recipe to account for the sweetened kind.
Here's the final version of the recipe, as distributed. I imagine that if a bunch of LTHers were to bake these, and post photos, we'd find substantial differences as well.
A N Z A C biscuits
ANZAC stands for Australian-New Zealand Army Corps. "Biscuit" is what Aussies call a cookie. ("Scone," pronounced "skawn," is what they call our sort of biscuit.)
These sweet, slightly chewy cookies, which travel and keep extremely well, were sent to soldiers during World War I, and are still very popular.
This recipe has been adapted to modern American ingredients and measurements. Golden syrup, a mild-flavored, cane-sugar syrup popular in Britain and Australia, is widely available in the Southern U.S. (though it often is a mixture of corn and cane syrup); in the North, it may be found at gourmet shops and import stores (usually the pure-cane Lyle's brand, imported from Britain). Use it if you can; otherwise corn syrup makes an adequate substitute. If you can't find flaked coconut, shredded coconut can be chopped finer in a food processor or blender.
1 cup old-fashioned rolled oats*
1 cup all-purpose flour
1 cup flaked coconut (not shredded)
1 cup firmly packed dark brown sugar (or half brown and half granulated)
2 tablespoons golden syrup or dark corn syrup
1/4 pound butter (1 stick)
1 teaspoon baking soda
2 tablespoons boiling water
Preheat the oven to 325 degrees. Grease several cookie sheets. (If you like, line the cookie sheets with foil, dull side up, and grease that; this makes doing multiple batches a bit faster, since you can lift off the foil with the cookies on it and reuse the baking sheet without waiting for the cookies to cool.)
Combine the oatmeal, flour, coconut and sugar in a large bowl. Mix well, rubbing out brown sugar lumps with your fingers. Do not use an electric mixer.
In the microwave, melt the butter and syrup together in a medium bowl, about 2 minutes on high. (Or use a medium saucepan over low heat on the stove.) In a small bowl, dissolve the soda in the boiling water and stir the mixture into the syrup. Add the syrup mixture to the dry ingredients.
Mix well with a wooden spoon. Form well-rounded teaspoonfuls into small balls and place on the prepared cookie sheets. The dough should be very moist and slightly sticky. If it doesn't stick together well when you try to roll balls, add a bit more water. The cookies will spread a good deal -- leave plenty of space. A dozen cookies per baking sheet is about right.
Bake, two cookie sheets at a time, until the cookies are flattened and deep golden brown, about 12 to 15 minutes. Let the cookies cool on the baking sheets for a few minutes until they firm up, then transfer with a spatula to wire racks to cool completely.
Store in an airtight container with waxed paper between each layer of cookies. They'll keep at least a week at room temperature, and they freeze very well for longer storage.
Makes about 4 dozen small cookies. (The recipe may be mixed in double or triple batches, but bake only two sheets-full at a time, unless you have a convection oven.)
* Note: Use of quick oats will make a thinner, crisper, lacier cookie -- very tasty, but not, we are told, authentic. These will spread even more than the others.
I prefer the air-cushioned style of baking sheet for more even baking. If you don't have this kind, stacking two sheets atop each other and/or lining with foil will also prevent burned bottoms. Depending on your oven, you may also want to encourage more even baking by swapping around the cookie sheets midway through baking.
Measure ingredients carefully. Spoon flour and oats lightly into a dry measuring cup and level off with a knife. Use a spatula to scrape the golden syrup from the measuring spoon.
More water may be needed, depending on the dryness of your flour, etc.