Sift flour, powdered sugar, and salt. Rub in cold butter until sandy. Mix in egg yolk and cold water, then briefly knead into dough. Chill for 30 minutes.
Roll out to 3 mm thick, cut circles, and fit into tartlet molds. Blind bake at 180°C for 10 minutes, then 7–10 minutes until golden. Cool.
For Blueberry Compote
Heat blueberries, sugar, and lemon juice until soft. Add cornstarch mixture, cook 1–2 minutes until thickened. Cool.
For Diplomat Cream
Heat milk with vanilla. Whisk egg yolks, sugar, and cornstarch. Gradually mix in hot milk. Cook until thickened, then stir in butter and cool. Fold in whipped cream.
Assemble the Tartlets
Spread blueberry compote in cooled shells. Top with diplomat cream and smooth. Decorate with fresh blueberries and a dusting of powdered sugar.
Chill for 1–2 hours before serving.
