In a small saucepan, combine granulated sugar, water, a cinnamon stick, and lemon peel. Bring to a simmer over medium heat, stirring until sugar dissolves, about 3-4 minutes. Remove from heat and allow to infuse for 10 minutes.

In a medium saucepan over low heat, whisk together a bit of whole milk with all-purpose flour until smooth. Gradually add the remaining milk and cook while whisking until thickened, approximately 5-7 minutes. Combine with cooled syrup.

In a separate bowl, whisk together egg yolks and vanilla extract. Gradually add warm milk mixture to egg mixture while whisking constantly. Strain mixture through a fine mesh sieve.

Preheat oven to 550°F (290°C). Roll out puff pastry and cut into 12 circular pieces. Press each piece into greased muffin tin.

Pour prepared custard into each pastry shell, filling them about three-quarters full. Bake for 12-17 minutes or until tops are golden.

Remove tarts from oven and cool in muffin tin for about 5 minutes before transferring to a cooling rack. Serve warm, optionally dusted with powdered sugar.