Pulse together the flour and powdered sugar until combined. Add butter and process until crumbly. Mix in egg yolk and water until dough forms. Chill for 30 minutes, preheat oven to 350°F, roll out dough, press into tart pans, and bake for 10–12 minutes.

In a saucepan over medium heat, whisk together lemon juice, lemon zest, sugar, and eggs. Stir for 8–10 minutes until thickened. Mix in butter until melted. Pour into cooled tart shells and chill for 1 hour.

In a heatproof bowl, combine egg whites, sugar, and cream of tartar over simmering water. Whisk until warm and sugar dissolves. Beat with an electric mixer until stiff peaks form. Stir in vanilla and food coloring.

Pipe the meringue onto the tarts, creating swirls or peaks. Use a kitchen torch to toast the meringue tips until lightly browned. Garnish with edible lilac petals or dried lavender.