Cut butter into ½-inch cubes and keep cold in the refrigerator.
In a large bowl, whisk to combine flour and salt. Add butter, toss to coat in flour, then use your fingers or a pastry blender to cut the butter into pea sized pieces.
Add 6 tablespoons of the cold water mixture and stir until a shaggy dough forms. Bring the dough together with your hands, adding a few more tablespoons of water if still crumbly. Turn dough out onto a floured work surface and pat into a fat disc. Wrap in plastic wrap and refrigerate for at least 2 hours.
On a lightly floured surface, roll out dough into a 12-inch circle. Carefully transfer to a 9-inch pie dish and crimp edges as desired. Use a fork to prick the bottom all over then freeze for at least 30 minutes.
When ready to prebake the crust, preheat oven to 375° F.
Line the crust with parchment and fill with dried beans or pie weights. Bake for 35 minutes. Carefully remove the parchment paper and weights and bake another 10-15 minutes until golden all over.
Remove crust from and reduce oven to 350° F.
Lemon Lavender Filling
Combine yolks in a medium bowl and whisk to combine. In a medium saucepan, combine sugar, cornstarch, lemon zest, lemon juice, water, lavender and salt. Bring mixture to a boil, whisking constantly, and continue to cook until thickened, about 5 minutes.
Reduce heat to low and slowly whisk in about ½ cup of hot mixture into egg yolks to temper. Return mixture to saucepan and bring to a boil, whisking constantly. Cook another 3-4 minutes until mixture is thick and bubbly. Remove from heat and stir in butter.
Strain mixture into warm pre-baked pie crust and set aside. Make meringue while the lemon filling is still hot.
Place egg whites, cream of tartar and salt in an extra-clean mixing bowl of a stand mixer, fitted with a whisk attachment.
Beat on medium speed until the whites are loose and foamy, 2-3 minutes. Increase speed to medium-high and add granulated sugar slowly (1 tablespoon at a time), until egg whites are stiff and glossy.
Spread meringue on top of warm lemon filling. Make sure meringue reaches all the way to the edge of the crust.
Bake for 25-30 minutes, until meringue is golden brown and set. Let cool at room temperature for at least 1 hour, then chill for 3 hours before serving. Sprinkle with candied lemon before serving.