Line a 6-inch x 9-inch (15cm x 23cm) rectangle loaf pan with 2 layers of cling film, allowing extra cling film to hang over the sides. Set aside.
Prepare a small-medium pot and half fill with water, and bring to a simmer.
Meanwhile, in a large heat-proof mixing bowl, add egg yolks, whole egg, vanilla, and sugar.
Once water is simmering, sit the bowl with egg mixture into the pot, ensuring the bottom of the bowl isn’t touching the water.
Using a hand-held electric beater, beat the egg mixture over the steaming water for 5 minutes until the mixture is thick and pale, this can happen fast so keep an eye on your mixture, and scrape down the sides as needed.
Once thick and pale, remove from heat and set aside.
In a separate mixing bowl add thickened cream and using a hand-held electric beater, beat the cream to firm peaks.
Spoon half of the whipped cream into a thick egg mixture, and gently fold until combined. Add remaining cream and fold until incorporated.
Add raspberries and fold through until just combined, creating a raspberry swirl effect. Set aside.
Melt the dark chocolate over a double boiler or microwave until smooth.
Pour 1/3 of the cream mixture into the lined pan.
Drizzle over half the melted chocolate.
Pour another 1/3 of the mixture into the pan over the chocolate.
Drizzle over the remaining melted chocolate.
Pour in the remaining cream mixture and smooth out the top.
Fold over the excess cling film from the sides to cover the semifreddo, or cover with new cling film.
Place in freezer to set for 6-8 hours or preferably overnight.
Semifreddo will not be completely hard, it will be set, similar to a frozen mousse. Depending on the strength of your freezer will depend on how solid your semifreddo turns out.
To serve, remove the semifreddo by peeling away the top cling film. Carefully invert by turning the pan upside down and onto a serving platter. Lift the pan so the semifreddo pops out. Remove cling film completely.
Top with fresh cherries and a dusting of sifted icing sugar.
Slice, serve, and enjoy!
If your semifreddo is too solid to slice through, let it sit at room temperature for 5-10 minutes until it’s softer to slice through.