Flaky Portuguese Custard Swirls

In a bowl, combine flour, salt, and cold water. Mix with a wooden spoon until the dough comes together and pulls away from the sides of the bowl. The dough should be sticky, and you can adjust with more flour or water if needed.

Transfer the dough onto a well-floured surface, dust with a little more flour, and knead for 1 to 2 minutes to form a round. Cover and let it rest for 15 to 20 minutes.

Roll the dough into a 1/8-inch-thick square, dusting with flour as necessary. The dough should still be sticky.

Spread 1/3 of the butter over 2/3 of the square using a silicone spatula, leaving a 1/2-inch border. Fold the unbuttered side over the middle of the square and fold the opposite end over it like a letter. Straighten the edges as needed.

Turn the dough with a bench scraper to unstick it from the counter, dust with flour, and roll into a 1/8-inch-thick rectangle, carefully stretching the edges as needed. Spread another 1/3 of the butter over 2/3 of the dough. Fold into thirds, transfer onto a lined baking sheet, and freeze until the butter is slightly chilled, about 10 minutes.

Sprinkle the dough with flour and roll into a square a little over 1/8-inch-thick. Spread the remaining butter over the dough, leaving a 1- to 1 1/2-inch border on the top edge. Roll the dough into a log starting from the bottom edge. Dust with more flour and polish the ends as needed. Seal with plastic wrap and refrigerate for at least 2 hours, preferably overnight.

In a pot, combine sugar, water, cinnamon, and lemon zest. Boil over medium heat, without stirring, until the syrup reaches 100 degrees C. Remove from heat.

Preheat the oven to 288 degrees C. Grease a 12-cup muffin tin.

In a cold pot, whisk flour, salt, and cold milk together very thoroughly. Cook over medium heat, whisking constantly, until the milk thickens, about 5 minutes. Remove from heat and let it cool for at least 10 minutes.

Whisk egg yolks into the cooled milk. Add the sugar syrup and vanilla extract. Mix until combined. Strain the custard into a glass measuring cup.

Unwrap the dough and trim any uneven bits on the ends. Score the log into 12 even pieces using a knife, then cut through.

Place a piece of dough in each muffin cup. Dip your thumb lightly in some cold water, then press your thumb into the center of the swirl. Push the dough against the bottom and up the sides of the cup until it reaches at least 1/8 inch past the top.

Fill each cup 3/4 of the way with custard.

Bake in the preheated oven until the pastry is browned and bubbly, and the tops start to blister and caramelize, about 12 minutes.

Cool the tarts briefly and serve warm. Enjoy!