Macerate the strawberries. Tip the sliced berries into a bowl with the caster sugar and lemon juice. Stir gently, then leave for 10 minutes. You'll know they're ready when the fruit looks glossy, the sugar has dissolved completely, and a bright red syrup has pooled at the bottom of the bowl. The smell should be sweet and faintly jammy.

Whip the cream base. In your mixer bowl, combine the chilled double cream, icing sugar and vanilla. Beat on medium speed for about 60 seconds, until the cream thickens to soft peaks — it should hold a shape for a second before flopping over. Stop here; overwhipped cream turns buttery and won't fold smoothly.

Fold in the mascarpone. Add the softened mascarpone and beat on low for 15–20 seconds. The mixture will look speckled at first, then suddenly come together into a thick, glossy cream that holds a firm peak. If it feels stiff, add the milk a teaspoon at a time until it drops lazily off the spoon.

Build the first layer. Spoon a heaped tablespoon of strawberry jam into the base of each glass. Follow with a layer of broken shortbread, pressing it down lightly so it sits in the jam. Add a spoonful of macerated berries, then a generous dollop of cream. Repeat until you reach the rim, finishing with cream.

Top and chill. Arrange halved strawberries on the surface and tuck in a mint leaf if you have some. Cover each glass loosely with cling film and refrigerate for at least 30 minutes. The trifles are ready when the biscuits have softened slightly but still have a little bite — press a spoon through and you should feel gentle resistance, not a crunch.

Serve cold. These are best eaten within 4 hours of assembly. Beyond that, the shortbread dissolves entirely and you're left with a pleasant but mushy pudding. If you're making them ahead, keep the components separate and layer just before serving.