In a mixing bowl, combine flour, sugar, and salt. Add cold butter and mix until crumbly. Add egg yolk and mix until dough forms. Press dough into tart pan.
Bake crust for 15 minutes. Let cool.
In another bowl, whisk together sugar, eggs, lemon juice, lemon zest, and lavender. Stir in heavy cream.
Pour filling into cooled crust. Bake for 15 minutes or until set. Let cool before serving.