Step 1

Heat oven to 300°F. Line an 8x8x2-inch square baking pan with foil.

Step 2

In a small bowl, stir graham cracker crumbs, brown sugar and butter until a sandy mixture forms. Press gently and evenly into bottom of prepared baking pan. Bake 12 to 15 minutes or until crust is golden brown and set. Set aside to cool completely.

Step 3

In a medium mixing bowl, whisk together sweetened condensed milk, egg yolks, lime juice and 1 tablespoon lime zest until well combined. Pour carefully and evenly on top of cooled crust.

Step 4

Bake filling at 300°F for 30 to 40 minutes or until filling is still slightly jiggly but center is just set. Transfer pan to cooling rack to cool completely, about 2 hours.

Step 5

Once fully cooled, make the topping: In a medium bowl with an electric hand mixer, beat heavy cream, sugar and vanilla on medium-high speed until stiff peaks form. Spread whipped cream evenly over cooled bars. Sprinkle with lime zest for garnish, if desired. Cover and refrigerate at least 2 hours before slicing and serving. Use foil to help you remove the bars from the baking pan before slicing.

Step 6

Bars will keep, covered and refrigerated, up to 3 days.