Summer Fresh Key Lime Squares
1 cup plus 2-1/2 Tbsp. finely ground graham cracker crumbs
1/3 cup sugar
5 Tbsp. unsalted butter, melted
3 large egg yolks
1-1/2 tsp. finely grated lime zest (from 2 limes)
2/3 cup fresh Key lime juice
1 cup sweetened condensed milk (14 oz.)
Whipped topping to garnish
2 Key limes, thinly sliced into half-moons
1/2 cup toasted coconut (optional)
Preheat oven to 350°F. Prepare the crust by stirring the graham cracker crumbs, sugar, and butter together in a small bowl. Press evenly onto the bottom of a 2.5-qt. rectangular baking dish. Bake until golden brown, about 10 minutes. Remove from the oven (leave it on) and let the crust cool completely on a wire rack.
For the filling, put the egg yolks and lime zest in the bowl of an electric mixer fitted with the whisk attachment. Mix on high speed until very thick, about 5 minutes. Reduce speed to medium. Add condensed milk in a slow, steady stream, mixing constantly. Raise speed to high; mix until thick, about 3 minutes. Reduce speed to low. Add the lime juice and mix until just combined.
Spread the filling out evenly over the crust using a spatula. Bake until filling is just set, about 10 minutes, rotating dish halfway through. Let cool completely on a wire rack. Refrigerate at least 4 hours (or overnight). Cut into 1-inch bars. Dollop with whipped topping and garnish with a slice of lime and a sprinkle of toasted coconut, if desired.