Tangy Lime Bars

Instructions

Prepare and Bake the Crust

1. Preheat and prep pan: Preheat oven to 350°F. Line 8×8-inch pan with two sheets of foil, crossing one over the other and pressing into corners and up sides. Butter the foil generously.
2. Make shortbread dough: In medium bowl, use fingertips to massage lime zest into granulated sugar until fragrant oils are released and mixture looks like wet sand.
3. Add dry ingredients: Add flour, chopped mint, baking powder, and salt. Toss to combine.
4. Cut in butter: Add chilled butter pieces and toss to coat. Use fingertips to smash butter completely into flour mixture until you have moist crumbs that hold together when squeezed.
5. Press into pan: Transfer shortbread to prepared pan and scatter evenly. Use hands to flatten into even layer, working into corners and against sides.
6. Bake crust: Bake until lightly golden across surface (25-30 minutes). Remove from oven and let cool while making filling. Reduce oven temperature to 300°F.

Make the Lime Curd Filling

7. Heat citrus mixture: In small saucepan, combine lime juice, lemon juice, cornstarch, salt, and ½ cup (3.5 oz) sugar. Cook over medium heat, whisking occasionally to dissolve sugar.
8. Thicken: When mixture boils, whisk constantly until it thickens slightly from cornstarch (about 1 minute). Remove from heat.
9. Temper eggs: In medium bowl, vigorously whisk egg yolks, whole egg, and remaining ½ cup sugar until smooth, thick, and pale (about 1 minute). Whisking constantly, slowly drizzle hot citrus mixture into eggs a tablespoon at a time until you've added about half.
10. Cook curd: Whisk egg mixture back into saucepan. Set over medium-low heat and cook, whisking constantly, until curd turns opaque, is thick enough to coat back of spoon, and barely holds marks of whisk (it will register 170°F on thermometer), 3-5 minutes.
11. Add butter: Remove from heat and whisk in chilled butter one piece at a time, waiting until each melts before adding next, until smooth.

Bake and Chill

12. Pour and bake: Pour hot curd over crust and shake pan gently to settle in even layer. Bake until sides have puffed and center is set but still slightly wobbly when shaken (30-35 minutes).
13. Cool completely: Remove from oven and let bars cool completely in pan.
14. Chill before cutting: Transfer cooled pan to refrigerator and chill until bottom is cold to touch (about 1 hour). This hardens the butter, making it easier to remove and slice.
15. Cut and serve: Lift bars from pan using foil. Cut into 16 squares. Dust with powdered sugar and top with lime zest before serving.