Key Lime Bars

1 . Stage

Preheat the oven to 350 degrees F (175 degrees C). Line an 8-inch square baking pan with aluminum foil, then brush with melted butter. Place pan in the freezer until needed.

2 . Stage

Cream butter for crust in a bowl with an electric mixer. Beat in flour, brown sugar, and salt. If mixture does not hold together, knead it on a work surface. Place mounds of the mixture in the cold baking pan; press with your fingers to smooth it into a firm layer on the bottom.

3 . Stage

Bake in the preheated oven until lightly colored, about 18 minutes.

4 . Stage

While the crust is baking, prepare lime layer: pour 2 tablespoons regular lime juice into a small bowl. Discard any extra, or reserve for another use. Add lime zest and Key lime juice; mix to combine.

5 . Stage

Combine sugar, eggs, flour, and baking powder in a bowl; beat with an electric mixer at high speed for 1 minute. Stir in lime zest-juice mixture and food coloring.

6 . Stage

Remove crust from the oven and immediately pour lime mixture over top. Return to the oven and bake until top is light colored and custardy, 25 to 30 minutes. Remove from the oven and let cool, about 30 minutes. Move to the freezer and chill for 30 minutes.

7 . Stage

Remove from the pan and cut into 16 squares. Sprinkle confectioners' sugar on top.