Key Lime Pie Thumbprint Cookies
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.
- 9 graham cracker sheets (about 5 oz.; 1 sleeve)
- ¾ cup plus 1 Tbsp. (101 g) all-purpose flour
- 1¼ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt
- ½ cup (packed; 100 g) light brown sugar
- ½ cup (1 stick) unsalted butter, room temperature
- 1 large egg
- ½ tsp. vanilla extract
- ¼ cup (50 g) granulated sugar
- 1 large egg yolk
- ⅓ cup sweetened condensed milk
- 4 tsp. finely grated lime zest, plus more for serving
- 2 Tbsp. plus 1½ tsp. fresh lime juice
- Place racks in upper and lower thirds of oven and preheat to 350°. Pulse 9 graham cracker sheets (about 5 oz.; 1 sleeve) in a food processor until sandy crumbs form. Add ¾ cup plus 1 Tbsp. (101 g) all-purpose flour and 1¼ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt; pulse to combine. Transfer to a small bowl.
- Pulse ½ cup (packed; 100 g) light brown sugar and ½ cup (1 stick) unsalted butter, room temperature, in processor until creamy. Add 1 large egg and ½ tsp. vanilla extract and pulse just to combine. Add graham cracker mixture and process until dough comes together and forms a ball, about 45 seconds.
- Place ¼ cup (50 g) granulated sugar in a clean small bowl. Using a #40 cookie scoop (about 2 Tbsp.), portion out dough; roll into smooth balls (dough will be sticky). Working one at a time, toss balls in granulated sugar to coat generously. Divide between 2 parchment-lined baking sheets, spacing at least 2" apart (about 7 per sheet). Working one at a time, dip the bottom of a shot glass or ⅛-cup measuring cup into remaining granulated sugar, then press down in center of balls to create a divot that can hold 2 tsp. filling, about ¼" deep (for the first cookie, press glass into it a little before dipping into sugar; it will easily adhere to glass from thereafter). Chill cookies in freezer 15 minutes.
- While cookies are chilling, whisk 1 large egg yolk and ⅓ cup sweetened condensed milk in a small bowl to combine. Add 2 Tbsp. plus 1½ tsp. fresh lime juice and 4 tsp. finely grated lime zest; whisk until slightly thickened.
- Remove cookies from freezer and spoon about 2 tsp. filling into each divot (don’t overfill). Bake cookies, rotating baking sheets top to bottom and front to back halfway through, until filling is set and cookies are firm and golden brown around the edges, 12–14 minutes. Let cookies cool on baking sheets 5 minutes. Transfer to a wire rack and let cool completely.
- Just before serving, finely grate a little lime zest over each cookie. Do Ahead: Cookies (without lime zest) can be baked 1 day ahead. Store airtight in a single layer at room temperature.
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.