The Crust (for two tarts about 9”):

Blend ingredients 1 to 9 in a food processor and pulse until the dough clumps. If the mixture is very dry and crumbly even after pulsing, add a little water or if you like, lemon juice, just one tablespoon at a time. Dough will be soft, depending on how cold the butter was to start. Chill the dough for 30-60 minutes. If the dough is very cold, it will be quite stiff and you may want to wait until it is slightly malleable. Then roll the dough between two sheets of wax paper - half the dough at a time to more or less fit your pans. If the dough seems sticky, sprinkle a little flour on the dough or wax paper.

Preheat the oven to 400ºF.

Line bottom, but not the sides, of tart pans or spring-form pans (ideally with removable bottom) with parchment paper. Place dough in pans and if necessary, patch any holes and push dough along the sides of the pan. Trim with a knife for tidy edges. Dock the crust with a fork and bake oven until the dough is just barely golden, about 10 minutes.  Lower oven temperature to 320ºF.

The Filling (for two tarts about 9”):

Blend ingredients 10 to 13 together in a food processor or in a bowl with beaters, until it is smooth. Pour into the pre-baked tart pans. Bake at 320ºF for approximately 30-45 minutes until the top has risen slightly and is slightly browned. Baking times will be affected by the thickness of the filling! Remove from oven and immediately sprinkle the top with the zest/sugar mixture. As the tart cools, this topping will become crunchy. Let the tart cool completely before removing from pans and serving.

The Topping:
Chop the lemon zest with the sugar until fine (ingredients 14 and 15). Sprinkle chopped sorrel leaves as optional garnish.

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