For the shortbread, sift the flour, icing sugar and salt into a large mixing bowl. Add the diced butter, then rub the butter into the flour mixture using your fingertips until the mixture resembles breadcrumbs.
Make a well in the centre of the flour mixture, then add the egg yolks and work them into the mixture, drawing the dry ingredients into the wet ingredients gradually, until the mixture comes together as a dough. Be careful not to overwork the dough.
Shape the dough into a sausage using your hands, then wrap in cling film and chill in the fridge for at least two hours.
Meanwhile, for the gooseberry creams, place the gooseberries into a large, heavy-based saucepan, sprinkle over the sugar and pour in the elderflower cordial.
Bring the mixture to a simmer and simmer, uncovered, for 25-30 minutes, stirring regularly to prevent the mixture catching on the bottom of the pan. Set aside to cool slightly.
Blend one-quarter of the cooked, cooled gooseberries in a food processor to a smooth purée.
Heat the milk over a gentle heat in a separate saucepan. When the milk is hot, drain the gelatine leaves, squeeze to remove any excess liquid and add them to the milk, whisking until dissolved. Remove the pan from the heat.
Spoon 225ml/8fl oz of the gooseberry purée into a measuring jug (any leftover purée can be added to the reserved cooked gooseberries). Whisk the gooseberry purée into the hot milk, then whisk in the yoghurt until well combined.
Divide the mixture equally among four ramekins. Cover each ramekin with cling film and set aside to cool completely, then chill in the fridge until set (when set, the gooseberry creams should wobble slightly when tapped).
To cook the shortbread, preheat the oven to 190C/375F/Gas 5. Remove the shortbread dough from the fridge, unwrap and slice into thick, even slices. Arrange the slices of dough on a baking tray, then bake the shortbread in the oven for 15-20 minutes, or until crisp and golden-brown.
Meanwhile, for the strawberry salad, gently warm the vanilla syrup in a small saucepan. Place the quartered strawberries into a bowl, sprinkle over the thyme leaves, then pour over the warm vanilla syrup. Set aside until needed.
To serve, place one ramekin of gooseberry cream onto each of four dessert plates. Place a teaspoonful of the reserved cooked gooseberries on top of each gooseberry cream. Stack two shortbread alongside. Spoon a portion of the strawberry salad alongside.