Citrus Semifreddo

Ingredients

 * nonstick cooking spray
 * 4 ounces purchased amaretti cookies, crushed (about 20 small cookies) plus more for sprinkling
 * 3 tablespoons unsalted butter, melted
 * ½ cup sugar, plus ¼ cup
 * 8 large egg yolks
 * ¼ cup lemon juice
 * 3 tablespoons lime juice
 * 2 tablespoons limoncello
 * pinch salt
 * 1 lemon, zested
 * 1 llime, zested
 * 1 cup whipping cream

Directions

 * 1) Spray a 9 by 5 by 3-inch metal loaf pan with nonstick spray.
 * 2) Line the pan with plastic wrap, allowing the excess to hang over the ends and sides.
 * 3) Combine the crushed amaretti cookies and the melted butter.
 * 4) Put in the lined pan and press down to firm and form a crust.
 * 5) Whisk ½ cup of the sugar, the egg yolks, lemon juice, lime juice, limoncello, and salt in a large metal bowl to blend.
 * 6) Set the bowl over a saucepan of simmering water (do not allow the bottom of the bowl to touch the water).
 * 7) Whisk the egg mixture until it is thick and creamy, and a thermometer inserted into the mixture registers 160°F, about 5 minutes.
 * 8) Set the bowl of custard into another bowl of ice water to cool completely.
 * 9) Stir in the zest.
 * 10) Using an electric mixer, beat the cream and remaining ¼ cup sugar in another large bowl until firm peaks form.
 * 11) Using a large rubber spatula, gently fold the whipped cream into the custard.
 * 12) Spoon the mixture onto the prepared crust.
 * 13) Fold the overhanging plastic wrap over the custard and freeze until frozen, at least 8 hours or up to 3 days.
 * 14) Unfold the plastic wrap.
 * 15) Invert the semifreddo onto a platter and peel off the plastic wrap.
 * 16) Cut the semifreddo into 1-inch slices and sprinkle with crushed amaretti cookies and serve.