Preheat the oven to 350F.
Heat a pot over medium heat and add the butter. Once melted, add the diced onions and and mushrooms cook for 5 minutes until soft and fragrant and the mushrooms are lightly golden. Add the celery and carrots. Cook for another 3 minutes.
Add the flour and cook on low heat for 3 minutes. Slowly add the white and stock.
Simmer for 6 minutes and season with salt and pepper. Set aside to cool.
Place the puff pastry on a lightly floured surface and cut circles circles to fit the top of your cooked vessel. Make sure to leave extra dough for the edges.
Mix the crabmeat into the vegetable mixture and pour it into your ramekins or other cooking vessel.
Brush the edges of your vessel with egg wash and top with the puff pastry circle. Brush the top of egg wash and bake for 15-20 minutes until the top of golden brown.