Set the oven to 350°F before mixing the custard. This moderate heat gives the thick center time to cook while the outside browns.
Combine the two whole eggs and extra yolk in a wide, shallow dish, whisking until uniform. The mixture should show no distinct strands of egg white.
Pour the melted butter into the eggs gradually while whisking continuously. A well-blended mixture looks glossy rather than separated into oily patches.
Add the baking powder, milk, 2 tablespoons of sugar, and vanilla, then whisk thoroughly. The dipping custard should look evenly combined, with no visible pockets of baking powder.
Coat a rice paper sheet in custard, lift it out, and let loose liquid fall back into the dish. The wrapper should carry a coating without a puddle of custard hanging underneath.
Dip two more sheets the same way and align all three on a cutting plate. The layers will feel slippery initially, then begin clinging together as they soften.
Use a sharp knife or kitchen scissors to make two cuts from the circle’s top center toward its lower left and lower right edges. You should have a broad central triangle and two curved side pieces.
Lay one curved piece lengthwise over the triangle’s center and the other crosswise across its broad bottom edge. The arrangement should have a pointed top and a thicker, wider bottom.
Roll the layered shape from its wide bottom toward the pointed tip, then assemble the remaining croissants with the other sheets. Each roll should have a plump center with the triangle’s point wrapped around it.
Transfer the crescents to a parchment-lined baking tray, sprinkle the reserved teaspoon of sugar over them, and bake for 30 to 35 minutes until golden and crisp. Look for a crackly exterior and a set, chewy center rather than wet custard.