Line the base of a 1 kg loaf pan (22cm x 12cm / 9-inch x 5-inch) with cling film.
Chop the chocolate into small chunks, place them in a bowl and microwave for 30 second intervals until melted, stirring each time. Let it cool before proceeding with the recipe.
In a large bowl, whip the heavy cream until stiff peaks form and is firm, about 4-5 minutes.
Gently fold in sweetened condensed milk, melted dark chocolate, California Walnuts and cocoa powder. Gently stir with a spatula all the ingredients until combined.
Pour the semifreddo mixture in the prepared loaf pan and use a spatula to smooth the surface. Cover with cling film and freeze for at least 4-5 hours.
Remove from the freezer 10-15 mins before serving. Unwrap the loaf pan and turn the semifreddo upside down onto a serving platter.
Serve it straight away or decorate with strawberries, chopped chocolate and more California Walnuts.
