Lulu, I don't know if this will help because the names of the qualities one wants aren't scientific or universal: I learned in a class from a baking scientist (a friend dragged me there but I learned some good stuff!) that a teaspoon of water in a regular batch of cookies (i.e., several dozen average size) makes the difference between chewy and hard, all other things being equal. So when Nestle took the spoon of water out of the Toll House recipe on the package, they were opting for crisper than chewier.
Do be sure to use cane sugar. There are people who can successfully use beet sugar because they know how, but cookies are the most sensitive to different ingredients, and there's a 3% difference in the makeup between cane and beet sugar. Beet bakes up much drier. Also, regular cookie recipes assume granulated white sugar, not superfine (also called castor sugar or baking sugar) or raw or anything else. The brown sugar should be white cane sugar which has molasses added. Other kinds of sugar work differently. You can adapt recipes to them, but they're not likely to come out just right as written.
Basic American recipes also assume bleached white AP flour. They'll usually work out fine with unbleached, but the texture may be affected. The process of bleaching affects how it absorbs water.
The kind of butter you use makes a difference, too. Different butters have different water contents. High quality American style butters have a butterfat content of 82-83%, and the difference is reflected in the water content. European style butter has 85-86% butterfat, and American bargain butter has about 80% butterfat. Most American recipes are meant for the 82%. You can't tell from the per serving nutrition information, but even if your brand doesn't say what the percentage is on the package, they often will on their websites, or sometimes you can find it on baking or nutrition oriented websites. Usually, if it doesn't say, however, top brands are the 82% and discount brands are 80%. The Euro style ones will usually say that they are. Use the euro style for croissants and the American premium for cookies.
Baking margarine (inc. "vegan butter") is only suitable for cookies if it's sticks with 100 Calories per tablespoon. The others have too much water and/or other weirdness that might work fine on your baked potato but won't bake right. Margarine has a different sized fat globule and a much higher melting point. This greatly affects the texture of the cookies. Use butter if you want a melt in your mouth kind of cookie, and/or a crispier one. Also, if you're doing dough balls that are supposed to spread in the heat of the oven. Use margarine for drop cookies that spread less and hold the shape you make them better because of the higher melting point. This also lets you skip the chill before baking step that helps when you use butter. (The proportions of flour to fat, etc., in cut out cookies are generally such that they hold their shape even with butter.) When I make flat chewy Toll House, I use The Expert's method: Make a quenelle of cookie dough, place it on the sheet, then flatten with the back of the spoon.
The Expert, who is famed amongst those who know for his Toll House cookies, is also the one who contributed the instruction to pull the pre-flattened cookies out of the oven before the centers are set. If you wait for them to completely firm up they won't be particularly chewy. The edges should be firm, with the faintest hint of brown, when you take them out, and they finish up on the warm cookie sheet.
Finally, do make sure your oven is well calibrated. If it's too accurate, it might also affect older recipes and need to be adjusted down a little. If it's an older or less precise oven with a greater variation of actual temperature, the setting and/or time may be affected. Even so, each oven is different. Don't just follow the recipe on that. Get to know your own oven, and what timings and temperatures give you your desired results. An extra minute can also be the difference between chewy and hard.
I don't know if this addresses your problem, but most often with cookie issues it's because of the ingredients being different or the bake time/heat not being watched..
Good luck!
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Chocolate Chip Cookie Tips
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