Nestle Toll House Cookie Recipe

Check your baking soda, that is most likely the problem. But the weather isn't helping either! Also, if you want a thicker, chewier cookie use bread flour, not all purpose.

Jen is right on - cookies made with butter are flatter and crispier whereas shortening makes them lighter and more airy. You could try adding nuts to avoid the 'spread'.

My toll house cookies are always flat and crisp when I use butter. It has a lower melting temperature than margarine or shortening, so the cookies spread on the pan before they start to set in the oven. Mix the butter half-and-half with shortening or margarine and they will be fluffier. (I like them flat, myself.) Or you could try chilling the mixed batter before baking - that might keep them from spreading as quickly when they bake.

I'd try 2 things...
check your baking soda - how old is it? If it's more than 1 year or so, replace it.

adjust the amount of flour you're using. New brown sugar has more moisture than older brown sugar. Also, eggs can be bigger or smaller, so this can add more/less moisture. You may need to add up to 1/4 cup extra flour to compensate. You can try baking a "test cookie" (just bake 1 in your first batch) and if it comes out flat add about 2 Tbs flour, mix, and bake another tester. Repeat until it looks right.

Also, do you melt your butter, or do you cream it in with the sugar? This will change the texture too. I cream mine with sugar, then add eggs, then flour and baking soda.

If you melt the butter fully before adding it to the batter and then let it "set up" for a few minutes before putting cookie dough on the cookie sheets it helps too.