Reserve 1 tbsp sugar. Mix together the custard, creme fraiche, remaining sugar and vanilla in a large bowl. Put the bowl in the freezer, then leave for 1 hr until the mixture starts to freeze around the edges. Whisk the mixture to break down the ice crystals, return to the freezer for 1 hr or more, then repeat the whisking.
Meanwhile, cut a large food bag down one side and along the base and open out. Lightly oil a large loaf tin, ice-cream tub or food container, approximately 2 litres in capacity. Line with the plastic. Using a fork, lightly crush half the raspberries with the reserved sugar.
Spoon one-third of the semi-frozen custard into the tin. Sprinkle over half the meringues and half the crushed raspberries. Spoon over 3 tbsp coulis. Cover with another third of the custard and then the remaining meringues, raspberries and another 3 tbsp coulis. Pour over the remaining custard, then put in the freezer for at least 4 hrs, or overnight. Can be frozen for up to 2 weeks.
To serve, transfer the dessert to the fridge for 30-45 mins to soften it. When ready to eat, turn the cake out onto a dish, Scatter the raspberries over, then cut into thick slices and serve with a little coulis.