Step 1

Preheat oven to 375F.

Step 2

Spray an 8-inch or 9-inch square pan with cooking spray and line with parchment paper.

Step 3

Combine graham cracker crumbs, butter, and sugar in a small bowl and stir until combined.

Step 4

Press the graham cracker crumb mixture into the bottom of the prepared pan and press down firmly. Use the bottom of a measuring cup to really pack it in.

Step 5

Bake the graham cracker crust for 7 minutes. Remove from the oven and let cool.

Step 6

Preheat the oven to 350F.

Step 7

Whisk the sweetened condensed milk, egg yolks, lime juice and zest together in a medium bowl.

Step 8

Pour over cooled crust and bake for 25 minutes. Let the bars chill before serving.

Step 9

Dust with powdered sugar and sprinkle with additional zest if desired. Cut into bars.

Step 10

Store in an airtight container in the refrigerator.