First, make the base. Heat the oven to 200C/180C fan/gas 6 and line a 20 x 20cm square tin with baking parchment, leaving it overhanging the sides. Beat the butter and sugar using an electric whisk until fluffy. Sift over the flour and cornflour, and stir to make a dough. Press into the tin, making sure it’s level. Prick all over using a fork and bake for 15-20 mins until set and lightly golden. Cool completely in the tin.

Meanwhile, tip the cream and vanilla into a saucepan over a low heat. Warm until starting to steam. Combine the egg yolks, caster sugar, cornflour and plain flour in a heatproof bowl to create a thick paste. Slowly pour in the warm cream, whisking until combined.

Put the gelatine in a small bowl and cover with cold water. Pour the custard mixture back into the saucepan, set over a medium-low heat and bring to the boil, whisking continuously until thickened, about 4-5 mins. When it’s very thick and bubbling, remove from the heat.

Squeeze the excess water from the gelatine and stir it into the custard until fully dissolved. Pour the custard over the shortbread base, smooth the surface, cover and chill for 3 hrs until set.

Arrange the strawberries over the set custard in overlapping lines, then brush with the warm jam for extra shine, if you like. Cut into nine large or 12 smaller squares to serve. Will keep chilled for up to two days, but best served the day of making.