Line a large loaf pan with plastic wrap. Leave enough plastic wrap over the edges to be able to cover the loaf at the end.

Coulis: Heat the sugar and water over medium heat til the sugar is dissolved. Put syrup and berries in the blender and puree. Strain mixture through a a fine mesh sieve. Add the liqueur.

Take ⅓ cup of the coulis and reserve the remainder until ready to serve.

Beat the cream and sugar until it forms soft peaks. Beat the sour cream in a separate bowl until it is fluffy. Gently fold the sour cream into the whipped cream. When evenly mixed add the ⅓ cup of raspberry coulis and swirl it through the mixture loosely.

Pour into the loaf pan. Fold the excess plastic wrap up to seal the mixture. Freeze at least 4 hours and up to 3 months. When ready to serve slice the semifreddo, drizzle each slice with raspberry and garnish with a few fresh raspberries.