Step 1

Line a sheet pan with parchment paper. Butter the wells of two large six-cup popover pans, then generously sprinkle each well with sugar.

Step 2

Generously flour your work surface. Cut the croissant dough into six equal pieces. Leave one on your work surface and place the remaining five on the sheet pan. Cover loosely with plastic wrap and refrigerate until ready to use, one at a time. Roll out the first piece until it’s as long, wide, and thin as possible, about 8 by 18 inches [20 by 46 cm]. Brush with some of the melted butter and sprinkle with 1 heaping Tbsp. of the granulated sugar, pressing it into the butter gently to adhere. Starting from a short edge, roll up the dough into a log, then cut the log in half lengthwise, so the layers of dough and filling are visible. One at a time, fold each half of the dough in half with the layers fanning out, so it’s in a horseshoe shape. Twist one side of the horseshoe over the other, making a loop. Place the ends of the dough into one of the wells in the prepared popover pan so the ends are resting on the bottom and the top loop is sticking out slightly. Repeat with the other horseshoe. Repeat with the remaining five pieces of dough, for a total of twelve cruffins.

Step 3

Cover the pans loosely with plastic wrap and let the dough rise at room temperature until doubled in size and it feels like a marshmallow when pressed, 2 to 3 hours. (Cruffins can also do a slow rise in the refrigerator overnight. See note for overnight cruffins.)

Step 4

Position an oven rack in the middle of the oven and preheat the oven to 400°F [200°C]. Line a sheet pan with parchment paper. Put some sugar in a shallow dish.

Step 5

Remove the plastic wrap from the pans and bake the cruffins until they are golden brown, 25 to 35 minutes. Let the cruffins sit in the pans for 1 to 2 minutes, then flip them out onto the prepared sheet pan. Roll each cruffin in the sugar, and transfer to a wire rack to finish cooling.

Step 6

Split the vanilla bean in half, scrape the seeds out into a small dish, and put the pod in a medium, heavy-bottom saucepan. Add the milk and heavy cream and heat over medium-low heat until just about to simmer. Remove from the heat, cover the pan, and set aside.

Step 7

In the bowl of a stand mixer fitted with a paddle, beat the egg yolks on low speed until combined. Slowly add the granulated sugar, followed by the salt and vanilla bean seeds. Increase the mixer speed to medium-high and beat the egg-sugar mixture until very thick and pale yellow, about 5 minutes. Scrape down the sides of the bowl, lower the mixer speed to low, and beat in the cornstarch.

Step 8

Pour the hot milk and cream into a medium liquid measuring cup, leaving the vanilla bean pod behind in the pan. With the mixer still on low speed, very slowly add the hot mixture, beating until completely incorporated. Transfer the mixture to the saucepan and cook over medium-low heat, stirring constantly with a wooden spoon, until the pastry cream becomes very thick and begins to boil, 5 to 7 minutes. Switch to a whisk and whisk the pastry cream until glossy and smooth, 3 to 4 minutes. Remove from the heat and strain the pastry cream through a fine-mesh sieve into a medium heatproof bowl. Stir in the butter and vanilla.

Step 9

Lay a sheet of plastic wrap directly on the surface of the pastry cream to keep it from forming a skin and refrigerate until well chilled. Do ahead: The pastry cream will keep, covered in the refrigerator, for up to 5 days.

Step 10

Fill a piping bag fitted with a plain tip with the pastry cream. Gently push the tip into the top of the cruffin (find a divot or space) and pipe in 1 to 2 tablespoons of pastry cream. Serve the cruffins the day they are made.