Make the tart shells by pulsing together flour and powdered sugar in a food processor, adding cold butter, egg yolk, and water until dough forms. Chill, roll out, and bake for 10-12 minutes.

Prepare the lemon curd by whisking lemon juice, lemon zest, granulated sugar, and eggs in a saucepan over medium heat until thickened, then stir in butter.

Make the lilac meringue by combining egg whites, superfine sugar, and cream of tartar in a heatproof bowl over simmering water, whisking until warm. Beat until stiff peaks form, and fold in vanilla and food coloring.

Toast and garnish by piping meringue on chilled tarts, lightly toasting with a kitchen torch, and garnishing with edible flowers before serving.