You may have gathered that I LOVE key limes. I particularly adore these cookies, which are better than any commercial variety. I had to get the key-lime extract from a mail-order company, Silver Cloud Estates (1-410-484-4526), since the closest retail store was in Troy, New York. Fortunately, a small bottle of the stuff will last for quite a while! And the cookies are definitely worth the effort.
1 cup (2 sticks) sweet butter at room temperature
3/4 cup white sugar
3/4 cup firmly packed brown sugar
2 eggs at room temperature
1 tablespoon key-lime extract
1 teaspoon baking soda
1 teaspoon salt
2-1/4 cups flour
2 cups (12 ounces) white chocolate chunks (purchased or cut off a bar of white chocolate; use chips instead of chunks if you must)
Beat the butter and sugars together until they are smooth and creamy. Beat in the eggs, 1 at a time, followed by the extract, baking soda, and salt. Stir in the flour. Gently mix in the chocolate chunks.
Chill the dough, well covered and sealed, for at least 12 hours and preferably for 24 or 36. I got this trick from an article published last July in The New York Times in which experts weighed in on the perfect chocolate-chip cookie. The article argued that the best CCCs chill for an extended period of time so that the eggs can sink into the flour. The chilling really does improve texture and (somehow!) flavor.
About 15 minutes before you are ready to bake your cookies, preheat the oven to 375 degrees. Drop the cookies in teaspoon-sized rounds onto parchment- or silicone-covered baking sheets. Bake them for 10 to 12 minutes, until they are a golden brown. Let them cool briefly on the sheets; then remove them to a rack to cool.
Makes about 60 cookies.