While the weather may be (in)famously temperate, you can almost always tell what season it is in Southern California by the produce at the markets. Come the shorter, if not much colder, days of winter, stacks of local citrus are everywhere. And yet, every year while I was growing up, my grandfather was sure to send a generous gift box of softball-size ruby red grapefruits nestled alongside navel oranges, seedless mandarins, and bags of Key limes straight from Florida to my family in Santa Monica. A handful of the oranges would be sure to find homes in the toes of our stockings hung by the fireplace. Grapefruits were sliced open and served under thick layers of crunchy granulated sugar. And Key limes? They were most certainly destined for pies. While these cookies invert the classic ratio of crust to custardy filling (these are for you, crust lovers), they’re an affectionate homage to the dessert I associate most with the holiday season, and my lovingly stubborn grandpa. Blitzed graham crackers and all-purpose flour come together in a buttery, brown-sugar-sweetened dough that stays soft and chewy after baking. In the center of each thumbprint, a dollop of silky, tart lime filling sets during the cookies’ brief stint in the oven, just like their full-size namesake.
Yes, I’ve cheated here and used regular limes. Real Key limes will lend an extra sour tang and more complex floral citrus aroma to your cookies, but they’re admittedly fussier to zest and juice than the standard variety. You’ll need about 10 Key limes to make the filling, which you can find at Say Weee (starting at $3.99 per pound), or your local grocery store.
I don’t recommend bottled Key lime juice (it’s often rather astringent).
BAKER’S NOTE: Chilling the shaped cookies in the freezer before filling is a crucial step as it keeps the butter-rich dough from spreading too much when baking. Plus, it gives you just the right amount of time to whisk up the filling so it’s perfectly thickened, making it easy to portion. Because of its concentrated, toasty flavor, Heilala x Bon Appétit Double Fold Vanilla (paste, $30 for a 2.29-oz. jar, or extract, $27 for a 1.69-oz. bottle; heilalavanilla.com) is our favorite to bake with.