In a medium saucepan, combine fresh raspberries, sugar, and water over medium heat. Stir while it simmers for about 5-7 minutes until the raspberries break down. Mix cornstarch with a small amount of water until smooth, then add it to the simmering mixture, stirring until thickened.

In a heatproof bowl, whisk egg yolks and sugar until it reaches a ribbon stage, about 4-5 minutes. Place over simmering water, stirring for 8-10 minutes until slightly thickened. Add chopped white chocolate and stir until melted. Let cool.

In a chilled bowl, whip heavy cream until stiff peaks form, approximately 3-4 minutes. Be careful not to overwhip.

Gently fold the whipped cream into the cooled egg and white chocolate mixture. Start with a small amount to lighten, then gradually add the remaining cream.

Line a loaf pan with plastic wrap. Layer the cream mixture, raspberry filling, and crushed biscuits until finished, sealing with plastic wrap.

Cover with plastic wrap and freeze for 4-5 hours or overnight until firm.

Let the semifreddo sit at room temperature for 5-10 minutes to soften. Lift it from the pan and slice with a warm knife.