Make the Raspberry Coulis: In a small saucepan, combine the 400g of raspberries, caster sugar, lemon juice, and water. Set it over a medium heat and bring to a gentle simmer, stirring occasionally. Cook for about 5-7 minutes, until the raspberries have completely broken down and the sauce has thickened slightly.

Strain and Cool the Sauce: Remove the pan from the heat. Place a fine-mesh sieve over a bowl and push the raspberry mixture through it using the back of a spoon to remove the seeds. This step is a bit of a faff, but it gives you a wonderfully smooth coulis. Stir in the lemon zest and the optional liqueur, if using. Set aside to cool completely.

Whip the Cream: While the sauce cools, make the mascarpone cream. Pour the very cold double cream into a large mixing bowl. Using an electric hand whisk, beat the cream until it forms soft peaks. Add the sifted icing sugar and vanilla paste and continue to whisk until it holds stiff peaks. Be careful not to over-whip it, or it will turn grainy.

Combine with Mascarpone: In a separate large bowl, briefly beat the room-temperature mascarpone with a spatula just to loosen it. Add about a third of the whipped cream to the mascarpone and gently fold it in to lighten the cheese. I find this prevents the final mixture from becoming lumpy. Gently fold in the remaining whipped cream until you have a smooth, homogenous mixture with no streaks.

Begin Assembling: Pour about half of the cooled raspberry coulis into a shallow dish. Take one savoiardi biscuit at a time and dip it into the coulis for just 1-2 seconds per side. Don't let it get waterlogged! Arrange the dipped biscuits in a single layer in the bottom of a 20x30cm (approx. 8x12 inch) trifle dish or glass baking dish.

Create the Layers: Spread half of the mascarpone cream mixture evenly over the layer of biscuits. Scatter half of the fresh raspberries over the cream. Repeat the process: dip the remaining biscuits in the rest of the coulis, arrange them on top of the cream, and finish with the remaining mascarpone cream, smoothing the top with a spatula.

Chill and Set: Cover the dish with cling film and place it in the refrigerator to chill for at least 4 hours, but preferably overnight. This is the crucial step where the magic happens – the biscuits soften, and the flavours meld into a cohesive, delicious whole.

Garnish and Serve: Just before serving, decorate the top of the raspberry tiramisu with the remaining fresh raspberries and a few fresh mint leaves, if you like. A light dusting of icing sugar also looks lovely.