Heat oven to 220C/fan 200C/gas 7 and lightly flour a baking sheet. Put the flour, butter, sugar, half of the vanilla seeds and ¼ tsp salt into the bowl of a food processor, then pulse until fine. Tip into a large bowl. Beat the milk, egg and a good squeeze of lemon together, then tip into the bowl and bring together with a knife, using a cutting action, until you have a clumpy dough. Finally bring together with your hands if you need to.
Lightly flour the work surface, tip the dough onto it, then quickly shape into a smooth-ish disc. Using a rolling pin, pat out to 2cm thick. Cut out 8 rounds with a smooth 7cm cutter (you’ll need to pinch together the trimmings). Glaze just the tops with beaten egg, transfer to the floured sheet, then bake for 10-12 mins until risen and golden, and they sound
hollow when tapped on the bottom. Cool on a wire rack.
Beat the remaining vanilla seeds and icing sugar into the clotted cream. It will get runnier at first, but keep beating and it will thicken again. To serve, slice the very top from each shortcake to give a flat surface, then spoon over about 1 tsp jam. Top with a good dollop of the vanilla clotted cream and finish with the strawberries.