In a food processor, pulse together all-purpose flour and powdered sugar, then add cold butter until it resembles coarse crumbs. Integrate egg yolk and iced water, blending until a dough forms. Chill for 30 minutes, roll out, press into tart pans, poke holes, and bake at 350°F for 10-12 minutes until golden. Cool completely.

In a medium saucepan, whisk together fresh lemon juice, zest, sugar, and eggs over medium heat until thickened, about 8-10 minutes. Stir in unsalted butter until smooth. Pour into cooled crusts and refrigerate for at least 1 hour.

Set up a heatproof bowl over simmering water and combine egg whites, granulated sugar, and cream of tartar, stirring until warm. Beat with an electric mixer until stiff peaks form. Gently fold in vanilla extract and violet food coloring.

Transfer the lilac meringue to a piping bag and pipe atop the chilled lemon curd, creating peaks and swirls.

Lightly toast the meringue swirls with a kitchen torch until golden, being careful not to burn. Garnish with edible lilac petals or lavender if desired.