Line a 9x5-inch loaf pan with plastic wrap, leaving a 2-inch overhang on all sides; set aside.
Place the strawberries and 3 tablespoons of the granulated sugar in a food processor and puree until smooth, about 10 to 15 seconds. Transfer the puree to a fine mesh sieve set over a bowl. Stir and press on the solids to extract as much liquid as possible; discard the solids.
Whisk together the remaining sugar and egg yolks in a medium bowl set over a pot of simmering water. Stir constantly with a heatproof rubber spatula until the mixture coats the back of the spatula or reaches 160 degrees F on an instant read thermometer. Remove the mixture from the double boiler and beat with an electric mixer on high speed until pale yellow and tripled in volume, about 3 minutes.
In a large bowl, beat the heavy cream and vanilla extract on medium-high speed until soft peaks form. Whisk one-third of the whipped cream into the egg mixture, whisking gently until smooth, then fold the mixture into the remaining cream with a rubber spatula until completely incorporated.
Pour half of the cream mixture into the strawberry puree. Gently fold together until thoroughly incorporated, then pour into the loaf pan and smooth the top. Fold the pistachios into the remaining cream mixture and pour evenly over the strawberry layer; smooth the top.
Fold the plastic wrap over the surface and freeze for at least 12 hours and up to 3 days. To serve, peel the plastic from the surface and invert the pan onto a serving plate. Unmold the semifreddo, remove the plastic and cut into slices.