I thought it was interesting to learn about exactly what the copyright laws are regarding recipes. According to the U.S. government, a list of recipe ingredients is considered a scientific formula or compound, and cannot be copyrighted.
However, the instructions for a recipe may possibly be protected by copyright laws. For example, if your recipe instructions are something like,
"Mix flour, eggs, butter, and sugar. Drop onto greased cookie sheets and bake at 400 degrees for 10 minutes."
then that may not be copyrighted, as it is not original, intellectual, or unique. There are only so many ways to say, "Mix x plus y."
However, if with your recipe you have written your own, extensive or literary directions, then it may be protected by copyright law. For example,
"I like to whip the sugar and butter with my stand mixer while I get everything else around. Then I carefully fold it all together, mixing gently. I form the cookies using..."
It's also considered proper etiquette to tell where you got the recipe, idea, or base recipe. You don't have to, but it's nice, if it really is a recipe from a cookbook and you only changed a couple minor things.
Personally, I feel that if I've taken a recipe and changed nearly half of the ingredients or proportions, and written the directions myself, then it's become "my" recipe. But I love to share "my" recipes. I feel it's quite a compliment when someone asks, "May I have your recipe?" and I am always willing to share. :)