Step 1: Prepare the Croissants

Before starting with the custard and ganache, prepare the croissants to hold the filling.

1. Use a wooden skewer to poke a hole on opposite sides of the upper back of each croissant.
2. Gently wiggle the skewer to hollow out the center without tearing the pastry. Set the croissants aside.

This step ensures there is enough space inside the croissant to hold the custard without causing the pastry to break.

Step 2: Make the Vanilla Custard

The custard filling is the heart of this dessert, providing a creamy contrast to the flaky croissant and rich chocolate topping.

1. In a small saucepan, whisk together the egg yolks, sugar, cornstarch, and salt until the mixture is smooth and free of lumps.
2. Gradually whisk in the light cream, ensuring there are no streaks of egg yolk.
3. Place the saucepan over medium heat and cook, whisking constantly, until the mixture thickens. This process takes about 4-6 minutes. The custard should coat the back of a spoon when ready.
4. Remove from heat immediately.
5. Add butter, one piece at a time, whisking after each addition until fully incorporated.
6. Stir in the vanilla extract.
7. For an extra smooth texture, strain the custard through a fine mesh sieve. This step is optional but helps remove any small lumps for a silky finish.
8. Let the custard cool slightly before transferring it to a piping bag fitted with a long nozzle tip.

Step 3: Fill the Croissants

1. Insert the piping tip into one of the prepared holes in each croissant.
2. Gently squeeze the piping bag to fill the croissant with custard. Repeat on the other side to ensure even distribution.
3. Use about one-third of the custard per croissant.

If any custard spills out, simply wipe it away with a damp paper towel. Avoid overfilling to prevent leaks.

Step 4: Make the Chocolate Ganache

Ganache adds the final, decadent touch to these croissants.

1. In a small saucepan, combine half & half (or light cream) with corn syrup, if using. Heat over medium-low until hot but not boiling.
2. Remove from heat and add the chopped chocolate. Stir continuously until the chocolate is fully melted and smooth.
3. Let the ganache sit for a few minutes to thicken slightly before using.

Alternatively, you can microwave the cream and corn syrup in a heatproof bowl for about 30 seconds, then stir in the chocolate until melted.

Step 5: Assemble the Dessert

1. Spoon the chocolate ganache over the filled croissants, covering the top evenly.
2. Sprinkle chopped nuts over the ganache while it is still wet so they adhere well.
3. Transfer the croissants to the refrigerator and chill for at least 1 hour before serving. This allows the custard to set and enhances the flavors.