Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.

Spread the chopped pecans on a baking sheet and toast for 5-7 minutes at 375°F (190°C), until fragrant and lightly browned. Set aside to cool.

In a medium saucepan, combine butter, brown sugar, heavy cream, light corn syrup, and salt. Cook over medium heat, stirring constantly, until butter is melted and sugar is dissolved.

Bring the mixture to a boil and cook for 3-5 minutes, without stirring, until caramel thickens and turns amber. It should coat the back of a spoon.

Remove from heat and stir in vanilla extract.

Slice each croissant horizontally, leaving a hinge. Brush insides with egg wash (optional).

Place bottom halves on baking sheet. Generously spoon warm caramel sauce over, spreading evenly. Sprinkle with toasted pecans.

Place top halves back on. Brush tops with egg wash (optional). Bake for 12-15 minutes at 375°F (190°C), until golden brown and caramel is bubbly.

Let croissants cool slightly on baking sheet before serving warm.