Adapted from a recipe on Epicurious.com by Tracey Seaman
10 oz shortbread cookies, broken into pieces
1/2 cup walnuts
1/2 stick butter, melted
1 # strawberries
1 # rhubarb
1/2 cup + 1/2 cup sugar
2 large eggs
1/2 cup mascarpone cheese
1 tsp vanilla extract
1 1/2 cups heavy whipping cream
Preheat the oven to 350°F. Add the shortbread pieces and walnuts to the bowl of a food processor. Process until finely ground. Transfer the shortbread-walnut mixture to a medium-sized mixing bowl, and add the melted butter. Stir to combine well with a rubber spatula. Press this mixture evenly across the bottom and about 1-inch up the sides of a 9-inch spring-form cake pan. Bake until golden, about 10 minutes. Cool on a wire rack.
Rinse the strawberries under cool running water. Remove the leaves and cut out the core. Thinly slice the strawberries.
Rinse the rhubarb under cool running water. Using a knife, trim off any leaves or blemishes on the stem. Slice length-wise down the middle of the stem, cutting the stem into 2-4 long and equal pieces of about 1/2-inch width. Then slice width-wise into half-inch slices.
Combine the sliced strawberries, rhubarb and 2/3 cup sugar in a medium saucepan. Turn the heat to medium and simmer, stirring frequently, until soft, about 5 minutes. Remove from the heat. Divide into two equal portions, each about 2-cups in volume. Set aside one portion to use as a sauce for the finished dessert. (Refrigerate in an air-tight container.) Set aside the other half to use in the next step.
Add the eggs and remaining 1/2 cup sugar to the bowl of a stand mixer. Whisk on high speed until foamy, about 3 minutes. Add that second half of the strawberry-rhubarb mixture to the egg-sugar mixture, and whisk to combine. Place the bowl over a medium-sized saucepan containing about an inch of simmering water. Mix constantly with a rubber spatula until a thermometer reaches 140°F. (This temperature just ensures that the eggs are safe to eat.) Remove from the heat and return the bowl to the stand mixer. Beat on high speed for 3 minutes. Allow the mixture to cool to room temperature, stirring occasionally. Transfer to a large mixing bowl, cover with plastic wrap, and chill in the refrigerator for at least 30 minutes.
Combine the mascarpone, vanilla and 1/4 cup cream in a clean bowl of a stand mixer. Using the paddle attachment, beat on low speed until combined. Gradually beat in the rest of the cream, then beat at medium-high speed until the mixture holds stiff peaks. Fold this mixture into the strawberry-rhubarb-egg mixture, mixing well to evenly combine. Pour this mixture over the crust in the spring-form pan, smoothing the top with a rubber spatula. Wrap well in plastic wrap and freeze, at least three hours.
Before serving, remove the pie from the freezer, unwrap, and allow to stand at room temperature about 20 minutes, to soften. Remove the sides of the pan and place the tart on a serving platter. Cut into 10 slices, and serve with a dollop of the reserved strawberry-rhubarb sauce on top.
SERVED AT THIS DINNER PARTY