In a food processor, combine all-purpose flour and powdered sugar, then add chilled unsalted butter. Pulse until the mixture resembles coarse crumbs, about 30 seconds. Mix in the egg yolk and ice-cold water gradually until a dough forms. Chill the dough for 30 minutes, then roll it out and fit into mini tart pans, prick the bases, and bake at 350°F for 10-12 minutes. Allow to cool.

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

Place egg whites, granulated sugar, and cream of tartar in a heatproof bowl over simmering water. Whisk until warm and sugar dissolved, about 5 minutes. Remove and beat with an electric mixer until stiff peaks form. Incorporate vanilla extract and violet food coloring.

Using a kitchen torch, lightly toast the tips of the lilac meringue until golden brown. Garnish with edible lilac petals or a sprinkle of dried lavender. Serve immediately.