Preheat your oven to 350°F (175°C). In a bowl, combine all-purpose flour and powdered sugar. Cut in cold butter until mixture resembles coarse crumbs. Stir in egg yolk and water to form dough. Chill for 30 minutes, then roll out, press into mini tart pans, prick with a fork, and line with parchment. Bake for 10-12 minutes until golden brown, then cool completely.

In a saucepan over medium heat, whisk together lemon juice, lemon zest, granulated sugar, and eggs. Stir continuously for about 8-10 minutes until thickened. Remove from heat, whisk in butter until smooth. Pour into cooled tart shells and chill for at least 1 hour.

In a heatproof mixing bowl, combine egg whites, granulated sugar, and cream of tartar over simmering water. Whisk until warm and sugar dissolves. Transfer to stand mixer and beat on high until stiff peaks form (about 5-7 minutes). Mix in vanilla extract and violet food coloring.

Using a piping bag, fill with lilac meringue and pipe generously onto each tart, creating peaks and swirls.

Lightly toast meringue tips with a kitchen torch until golden. Garnish with edible lilac petals or dried lavender sprinkles for an elegant finish.