Loosely cover the muffin pans with lightly greased plastic wrap.
Let the pastries rise for approximately 30–45 minutes.
They should become visibly puffier but don't need to double completely.
Meanwhile, preheat the oven to 350°F (175°C) using conventional/static heat.
Brush & Bake
Whisk together:
- 1 egg
- 1 tablespoon milk
Very gently brush the exposed dough with the egg wash.
Avoid flooding the chocolate layers.
Bake for approximately 25–30 minutes, until the tops are deeply golden and the centers are baked through.
If you're baking two muffin tins simultaneously, rotate their positions partway through baking if your oven heats unevenly.
Make the Vanilla Sugar Syrup
While the pastries bake, combine the water and sugar in a small saucepan.
Bring to a gentle simmer and cook for approximately 2–3 minutes, just until the sugar completely dissolves.
Remove from the heat and stir in the vanilla.
You don't need to reduce it into a thick syrup.
Brush the Hot Muffins
As soon as the pastries come out of the oven, lightly brush or spoon some warm vanilla syrup over each one.
Don't completely soak them.
You want enough syrup to give the surface a beautiful shine and keep the exposed layers tender while still preserving some crispness around the edges.
Let the pastries cool in their pans.
Fill With Nutella
Once the pastries have cooled enough to handle, create a small opening in the center of each spiral using the handle of a wooden spoon or the tip of a teaspoon.
Transfer Nutella to a piping bag.
Pipe approximately 1–2 teaspoons Nutella into the center of each pastry.
For a more dramatic center, slightly warm the Nutella before transferring it to the piping bag so it flows more easily.
Cool Before Removing
Allow the pastries to cool almost completely before carefully removing them from the muffin pans.
Because the chocolate-butter filling can caramelize around the edges, they're more delicate immediately after baking.
Run a small offset spatula or thin knife around any areas that have stuck before lifting them out.