Pulse flour and powdered sugar together in a food processor until combined. Add cold butter and mix until crumbly. Blend in egg yolk and enough water to form a dough. Chill for 30 minutes, then preheat oven to 350°F (175°C). Roll out and press into mini tart pans, bake for 10-12 minutes until golden.

Whisk lemon juice, lemon zest, sugar, and eggs in a saucepan over medium heat. Stir continuously for 8-10 minutes until thickened. Remove from heat and stir in butter. Pour curd into cooled tart shells and refrigerate for at least 1 hour.

Simmer water in a saucepan. In a heatproof bowl, whisk egg whites, sugar, and cream of tartar over simmering water until warm. Remove from heat, beat until stiff peaks form. Fold in vanilla extract and food coloring.

Pipe meringue onto tarts and use a kitchen torch to toast the tops until golden. Garnish with edible lilac petals or dried lavender, and serve chilled.