Puff Pastry Ingredients:
- 170 g unsalted butter, softened
- 220 g all-purpose flour, plus more for dusting
- 160 ml water
- 1.5 g kosher salt

Filling Ingredients:
- 200 g granulated sugar
- 160 ml water
- 1 cinnamon stick
- 240 ml whole milk, plus 90 ml (total: 330 ml), divided
- 60 g all-purpose flour
- 6 egg yolks

Directions
1. Prepare the Dough:
* Whisk butter until creamy.
* Combine flour, water, and salt; knead until tacky.
* Roll dough into a ½-inch-thick rectangle, rest for 15 minutes.
* Roll into a 15-inch square, spread a third of the butter, fold, and seal.
* Repeat with remaining butter, rolling into an 18-inch square.
* Roll into a log, wrap, and refrigerate for at least 2 hours.

2. Make the Filling:
* Boil sugar, water, and cinnamon stick for 1 minute, then let sit.
* Heat 1 cup plus 1 tablespoon milk until bubbles form.
* Whisk flour with remaining milk, then slowly add hot milk.
* Discard cinnamon stick, add sugar syrup, and cook until thickened.
* Whisk in egg yolks, strain mixture.

3. Assemble and Bake:
* Preheat oven to 260°C.
* Cut dough log into ½-inch slices, press into tart molds.
* Fill each shell with 1½ tablespoons of filling.
* Bake until golden brown and caramelized, about 15-20 minutes.