Make Tart Shells: Combine flour and powdered sugar, pulse in food processor. Add butter, pulse until crumbly. Mix in yolk and water, pulse until dough forms. Chill for 30 minutes, preheat oven to 350°F (175°C). Roll into mini tart pans, prick bases. Bake for 10-12 minutes until golden, cool completely.

Prepare Lemon Curd: In a saucepan, whisk lemon juice, lemon zest, sugar, and eggs. Cook over medium heat while stirring for 8-10 minutes until thick. Stir in butter until melted, pour curd into tart shells. Chill for at least 1 hour.

Make Lilac Meringue: Whisk egg whites, sugar, and cream of tartar over simmering water until sugar dissolves (4-5 minutes). Beat until stiff peaks form. Fold in vanilla and food coloring. Pipe onto tarts.

Toast and Garnish: Use a kitchen torch to lightly brown meringue tops. Garnish with lilac petals or dried lavender. Serve immediately or refrigerate until serving.