Preheat the oven to 350° and line an 8 x 8 inch baking pan with parchment paper. Leave a 2" overhang on all sides for easy removal.
Using a food processor, mix the flour, cornstarch, confectioners' sugar and salt. Pulse until combined. Add the butter and lavender and pulse until the mixture becomes coarse crumbles.
Place the mixture into your baking dish with parchment paper. Spread and press the mixture evenly across the bottom and going 1/2" up each side of the pan. Bake for 20-25 minutes or until light golden brown.
Once you've removed the crust from the oven, reduce the temperature to 325°.
Meanwhile, in a mixing bowl, beat the eggs, egg yoke and sugar until light. Beat in the lemon zest and juice. Add the flour and salt and mix until combined.
Pour the lemon mixture over the warm crust and bake for 20-25 minutes until set. Once set, allow the bars to come to room temperature, then cover and refrigerate for at least 1 hour before serving.
When they're ready to serve, lift and remove from the pan. Dust the top with confectioners' sugar. Slice into 12 small bars (or preferred size) and enjoy!