In a food processor, combine all-purpose flour, powdered sugar, and cold butter, pulsing until the mixture resembles coarse crumbs. Add the egg yolk and cold water, pulsing until just combined into a dough. Chill the dough for 30 minutes, then roll it out on a floured surface. Press the dough into mini tart pans and bake at 350°F (175°C) for 10-12 minutes, until the shells are golden. Let them cool completely.

In a medium saucepan, whisk together fresh lemon juice, zest, granulated sugar, and eggs. Cook over medium heat, stirring constantly for about 8-10 minutes, until the mixture thickens and coats the back of a spoon. Remove from heat and whisk in butter until smooth and glossy. Pour the lemon curd into the cooled tart shells, smoothing the top, and chill in the refrigerator for at least 1 hour to set.

In a heatproof bowl set over simmering water, whisk together the egg whites, granulated sugar, and cream of tartar until warm and the sugar has dissolved, about 3 minutes. Remove from heat and use an electric mixer to beat until stiff peaks form, approximately 5-7 minutes. Gently fold in vanilla extract and violet food coloring.

Using a kitchen torch, carefully toast the tips of the lilac meringue on each mini lemon tart until lightly browned. Garnish the tarts with edible lilac petals or a sprinkle of dried lavender before serving.