Mix the dough: Add flour, sugar, salt, lemon zest, and cinnamon to the bowl of a standing mixer.
Mix on low for 30 seconds. Add butter and mix on low for 2 minutes, the increase the speed to medium for 10 seconds.
At this point you will have no large pieces of butter and the flour will look like coarse cornmeal. (If not, mix for 30 seconds more on low.)
Blend together the egg yolk and milk.
Add the mixture to the dough and mix for 15 seconds, or just until the dough starts to clump together. You can also do this by hand by working the butter into the flour mixture with your fingers and then mixing the egg yolk and milk in with a silicone spatula.
Form a disc: Flour a board and dump the dough onto it. Using the heel of your hand, push the dough away from you, pressing and smearing it along the board. Then gather the dough up with a bench scraper. Do this a few times to work the dough into a cohesive and pliable mass.
Then shape the dough into a disc, cover it with plastic wrap, and let it rest in the refrigerator for 1 hour, or up to 2 days.
Heat the oven: When you are ready to make the tart, preheat the oven to 375F.
Roll out the dough: Then, line a baking sheet with parchment paper and take the dough out of the refrigerator. If the dough has been in for more than an hour, let it sit on the counter until it is pliable and ready to roll.
Once the dough is ready for rolling, put it on a well floured board, dust the top with flour and roll it out with a floured rolling pin.
The dough is sticky, so you will want to keep everything floured for easy rolling. Roll out the dough into a 13-14 inch circle. Don't worry about the edges. This is a rustic tart.
Once you have it rolled out, transfer the dough to the baking sheet and set it aside. Refrigerate the dough if your kitchen is very warm.