Preheat the oven to 350 degrees F. For the crust, cream the butter and sugar together in mixer until well incorporated.
In another bowl, add together the flour, salt and lavender. Add flour mixture to butter mixture with mixer on low and mix until just incorporated.
With floured hands, take dough and gather into a ball. Then flatten dough and form in a 9 x 13 baking dish, bringing up 1/2in on each side.
Allow to chill in refrigerator for 30 minutes.
For the filling, whisk together the eggs, sugar, lemon zest, lemon juice, and flour. Pour over the crust and bake for about 30 minutes, until the filling is set. Let cool to room temperature.
Cut into triangles and dust with confectioners' sugar.