1. Line a 9x5-inch loaf pan with a 12x20-inch piece of plastic wrap; the wrap should hang over the long edges by 4 inches, and it will not completely cover the short ends. Press the plastic into the corners. Set aside.
2. Cream: Place the bowl and beaters of your mixer in the refrigerator for 15 minutes to chill. Then, beat the heavy whipping cream on high speed until the cream forms stiff peaks, about 4-6 minutes. Gently fold in the vanilla. Place back in the refrigerator.
3. Zabaglione: Place a medium saucepan filled with about 2 inches of water on the stove and bring to a boil. In a heat resistant medium-size bowl, beat the egg yolks and 4 tablespoons of sugar with a whisk or hand mixer until combined.
4. Place this bowl on top of the water-filled saucepan and turn the heat to medium (water should not touch the bottom of the bowl). Beat continuously until mixture is thick and pale yellow. The batter should make ribbons as it falls off the beater/whisk, about 5 minutes. (You may need to remove the bowl occasionally from the heat to prevent the eggs from scrambling.)
5. Remove from heat and gently fold in the Cointreau, orange zest, and the ½ cup of pistachios. Set aside.
6. Meringue: In a clean mixing bowl with the beater, slowly beat the egg whites until foamy, about a minute. Then add the salt and cream of tartar. Increase the speed slightly and beat until soft peaks are formed, about 3-4 minutes. Turn off the mixer.
7. In a small saucepan with a lid, over medium-high heat, add the granulated sugar and water. Bring the mixture to a boil, swirling the pan until the sugar is dissolved. Do not stir! Cover with the lid and boil to the thread stage*, about 5 minutes, to make sugar syrup.
8. Turn the mixer back on to low and slowly add the sugar syrup. Once the syrup is incorporated, increase the speed to high and beat until the mixture is cool and shiny, stiff peaks are formed.
9. Using a large spatula, gently fold in ¼ of the meringue into the zabaglione. When almost completely incorporated, add the remaining meringue. Continue folding the mixture until fully incorporated.
10. Fold in the whipped cream.
11. Place the mixture into the prepared loaf pan and smooth out the top with an off set spatula. Cover the top with the plastic wrap and place in freezer for 8 hours.
12. To serve, unwrap the loaf and invert the loaf pan on to a platter. Pull down slightly on the plastic wrap as you lift the loaf pan. Remove the plastic wrap. If there are wrinkles, dip a knife or offset spatula into a little warm water and run over the surface to smooth them.
13. Garnish with the tablespoon of pistachios. Cut into slices and serve immediately.
TIPS & TRICKS
• *We are cooking the sugar and water together to make a sugar syrup. To test if your syrup has cooked enough, take a small amount of the syrup and drop it into a cup of cold-water. Little threads should appear.
• Carefully add the sugar to your egg whites, trying not to hit the beater as you add the hot syrup.
• You can test the temperature of the meringue by placing your hand on the bottom of the mixing bowl. When it is cool to the touch, the meringue is ready.
• This is called an Italian meringue. It also makes a fantastic icing for cakes & cupcakes.
• This semifreddo can be made several days in advance. Store in your freezer until ready to serve.