Preheat your oven to 500°F (260°C). Grease a standard 12-hole muffin tin generously with butter.

Lay the puff pastry sheet flat. If it is rectangular, roll it tightly from the short edge into a log. Cut the log into 12 even discs.

Place one pastry disc into each muffin hole, spiral side facing up.

Dip your thumbs in cold water. Press the center of the dough against the bottom and push it up the sides of the muffin cup to create a thin shell. The rim should be slightly thicker. Refrigerate the tin while making the filling.

In a medium saucepan, combine the milk, heavy cream, honey, orange zest, and the cinnamon stick. Bring to a gentle simmer over medium heat, then remove from heat and let steep for 5 minutes. Remove the cinnamon stick.

In a separate heat-proof bowl, whisk the egg yolks, cornstarch, and vanilla extract until smooth and pale.

Slowly pour the warm milk mixture into the egg mixture in a thin stream while whisking constantly to temper the eggs.

Pour the custard back into the saucepan and cook over low heat for 2-3 minutes, stirring constantly, until the mixture thickens enough to coat the back of a spoon.

Remove the muffin tin from the fridge. Pour the warm custard into the pastry shells, filling them about 3/4 full (do not overfill).

Bake for 12-15 minutes. The pastry should be golden brown and crispy, and the custard tops should be blistered with dark brown or black spots (this is traditional and desirable).

Remove from the oven and immediately sprinkle a tiny pinch of flaky sea salt over each tart. Let them cool in the tin for 5 minutes before transferring to a wire rack to serve warm.