In a medium saucepan, combine the split vanilla pod, milk, and 2 tablespoons (30 grams) of sugar. Heat over medium heat until just boiling.

In a separate bowl, whisk together the egg yolks, remaining 2 tablespoons (20 grams) sugar, and cornstarch until smooth and lump-free. Temper the eggs by gradually pouring the hot milk mixture into the yolk mixture while whisking constantly.

Return the mixture to the saucepan. Cook over medium heat, whisking continuously, until the cream thickens and bubbles gently, about 2 to 3 minutes. Remove from heat and whisk in the softened butter until smooth.

Transfer the pastry cream to a bowl and press plastic wrap directly onto the surface to prevent a skin from forming. Refrigerate for at least 3 hours until chilled and set.

In the bowl of a stand mixer fitted with the dough hook, combine the flour, sugar, and yeast. Mix on low speed and slowly add the lukewarm water. After 2 to 3 minutes, add the softened butter and salt. Continue kneading for about 10 minutes, until the dough is smooth, elastic, and slightly tacky but not sticky.

Transfer the dough to a buttered bowl, cover tightly with plastic wrap, and let it rise at room temperature until doubled in size, about 1 to 2 hours, or refrigerate overnight for slower fermentation.

Lightly flour your work surface and turn the dough out. Divide it into 8 equal pieces. Roll each piece into a small rectangle. Using a pasta machine set to thickness 5, roll each piece into a thin, long rectangle. If rolling by hand, roll as thin as possible, dusting with flour as needed to prevent sticking. Evenly spread 3 ounces (about 85 grams) of very soft butter over each rectangle, covering the entire surface. This butter layer is critical for the layered texture.

Starting from the shorter edge, roll the dough tightly into a log. Cut each log lengthwise down the center to create two long halves. Coil each half into a rose or snail shape, ensuring the butter layers face upward. Place each shaped cruffin into a well-buttered or greased muffin tin. Repeat with all pieces to make 16 cruffins. Let the cruffins proof until doubled in size, about 1.5 to 2 hours depending on room temperature.

Preheat the oven to 400°F (200°C).

Bake the cruffins for about 25 minutes, or until deeply golden brown and cooked through.

Remove from the oven and allow to cool in the tin for 20 minutes before carefully removing.

Dust with powdered sugar or fill with chilled pastry cream. To fill, create a hole in the center of each cruffin almost to the bottom using a small knife.

Fill a piping bag fitted with a round tip with pastry cream and pipe it into the center of each cruffin. Dust again with powdered sugar before serving.