Rhubarb Semifreddo

Preheat oven to 350ºF. Line a loaf pan with parchment paper. Press cookie crumbs onto the bottom. Bake about 15 minutes (will be crumbly).

Cook rhubarb and 1/4 cup sugar over medium heat until soft and juicy, about 10 minutes. Transfer to blender and puree until smooth. Set aside.

In a large metal mixing bowl beat egg and remaining sugar until foamy. Add rhubarb puree and beat until well mixed. Place bowl atop a saucepan of barely simmering water and beat at medium speed until temperature reaches 140ºF, about 5 minutes. Take off heat and continue beating for 3 minutes. Let cool to room temperature. Cover and chill 30 minutes.

In a stand mixer using the whisk attachment, combine 1/4 cup heavy cream, mascarpone cheese and vanilla extract. Gradually beat in the remaining cream until stiff peaks form. Fold whipped cream into the rhubarb custard. Fold in raspberries. Pour over cookie crumbs and freeze at least 3 hours.

To serve, gently lift parchment paper out of the loaf pan and cut semifreddo into slices. Garnish with lime zest.