Mix dough ingredient except butter in a stand mixer with a dough hook and let it run till dough forms a ball and pull away from the side of the bowl

Flour the work surface, gently push the dough into a 6 inch square, cover and let it rest for 20 minutes. 

In the meantime, whip the butter till smooth, and easily spreadable, almost like texture of mayonnaise

Roll the dough out to 18 inch square. Use a palette knife or spatula to spread 1/3 of the butter on left 2/3 of the square, leaving 1 inch around the edge un-buttered. Fold the right 1/3 of the dough over toward left. Then fold the left 1/3 over to cover the un-buttered dough. The result is 6 * 18 inch rectangle. Brush off excessive flour along the way. Also remove as much air as possible while folding. If it's warm, place the dough in frig for 10-15 minutes to harden the butter.

Place the dough long side toward you, roll from center to make an 18 inch square. Repeat the previous step to create 6 * 18 rectangle. Place the dough in refrigerator if necessary.

Roll the dough out to 18 * 22 inch. Spread remaining butter over the entire surface leaving 1 inch around un-buttered.

Starting with the shorter edge, roll the pastry into a tight log. Trim ends so the edges are even. Cut the log in half, and wrap with cling wrap tightly. Refrigerate at least 3 hours or overnight.

Take the chilled pastry log out of the frig and let it rest for 10 minutes. Roll the log to thinner and longer log, about 1 inch in diameter and 16 inches long. Cut 3/4 inch discs and place them cut side down in egg tart mold. 

Once the pastry dough is workable, dip thumb in water, flatter the dough spiral into the bottom to about 1/16 inches thick and push the dough up to slightly above the rim.

Place the tart molds in frig again for about 15 minutes.

In a small saucepan, bring sugar, cinnamon and water to a boil and cook until the mixture reaches 220F (100C). Remove from heat and let cool

In a medium bowl, mix flour and 1/4 cup of milk until very smooth.

In another small saucepan, bring 1 cup of milk to a near boil. Gradually add milk into flour mixture and whisk continuously.

Remove cinnamon stick and pour the sugar syrup slowly into the milk-flour mixture, whisking briskly. Pour hot mixture into the bowl holding egg yolks and whisk to combine. Strain the custard mixture and cover the surface with cling film and let it cool. Mixture can be made 3 days in advance.

Preheat over to 475F. Place pizza stone or cast iron pan on the top rack.

Fill tart with custard mixture to just below the rim.

Bake until the edges are golden brown and custard top shows small dark spots. For my relatively small tarts, it took 15 minutes.

Let cool in mold for 5 minutes before taking them out to cool on cooling rack.