1. In a mixing bowl, combine flour, powdered sugar, and salt. Cut in the chilled butter until the mixture resembles coarse crumbs. Stir in the egg yolk and enough cold water to form a dough. Roll out the dough, cut into circles to fit mini tart pans, prick the bases with a fork, and chill for 30 minutes.

2. Preheat the oven to 350°F (175°C). Bake the tart shells for 15–20 minutes or until golden brown. Let them cool completely.

3. In a saucepan, whisk together lemon juice, sugar, eggs, lemon zest, and vanilla. Cook over medium heat, stirring constantly, until thickened. Remove from heat and let cool slightly before pouring into the cooled tart shells.

4. In a clean bowl, beat the egg whites until soft peaks form. Gradually add the sugar, continuing to beat until stiff peaks form. Add lilac food coloring if desired and gently fold to combine.

5. Pipe or spoon the meringue onto the lemon filling in each tart. Use a kitchen torch to lightly brown the meringue or place under a broiler for a few minutes, watching closely.

6. Garnish with fresh mint leaves if desired and serve.