Preheat oven to 350 F. To make the crust, sift and whisk together the dry ingredients and add the melted butter to form a dough with claylike texture. Butter or spray a 9" or 10" tart pan with a removable bottom. Using your fingers, mold the crust along the bottom and up the sides. PRO TIP: Grease a flat-bottomed glass to even out the crust and get into the corners. Make sure to seal even the smallest cracks. They will let the filling flow under the crust and ruin your tart.
Chill the tart pan for 5 minutes. Dock the bottom with a fork, making marks that will prevent the pastry rising but be careful not to tear the crust.
Place non-stick parchment paper on top and fill with a layer of coins, beans, pasta, rice or anything that will slightly weigh down the pastry. I like coins because they get hot and cook on both sides, but you have to watch more closely to avoid overbaking.
Blind bake 15 minutes at 350 F then take out of the oven and let cool at least 2 minutes. Only remove the weights and parchment paper once cool enough not to tear the crust. Return to the oven uncovered and bake 3-5 minutes until the crust is a uniform golden brown. Be sure it is well baked and looks ready-to-eat because once you add the filling it will cook no further.
While the crust is doing its thing, make the filling by juicing fresh lemons, separating 4 egg yolks, and whisking together with 1 whole egg, sugar, salt. ginger, turmeric, and flour. Whisk through a mesh strainer to smooth out lumps but try to retain as much of the fresh ginger as you can.
This will blow your mind: Do not remove the crust from the oven. Make sure it is perfectly level with a stone or sheet pan underneath to catch any spillage. Use a clean watering can with a very long spout to pour the filling into the crust all the way to the top. Don't overflow the sides, you may have some filling leftover. Close the oven door and don't open it for at least 20 minutes. There is a special place you-know-where for bakers that open the oven door to check their tarts and let all the heat out.
Bake until the center still has a wobble (but not a jiggle) and the edges are set. Let cool to room temperature or chill in the pan. Then trim the crust, remove from pan, slice, and serve.