Preheat the oven to 350 degrees F. Roll out the puff pastry on a floured surface, to about 1/2-inch thickness. Using a round pastry cutter or cookie cutter, about 3 inches in diameter, cut out 6 round disks.
Brush each disk with the beaten egg, coating the pastry well. Arrange on a greased baking sheet and bake until the pastry rises and is golden brown, about 15 to 20 minutes. When baked, remove from oven and allow to cool.
Add the grapeseed oil to a large heavy-bottomed saucepan over medium heat. Add the onions and saute until soft and translucent (not caramelized), then add the lobster. Saute until the lobster is cooked, about 5 to 8 minutes.
At this point, add the carrots and celery and saute a few more minutes until the vegetables are tender.
Stir in the flour and cook for about 5 minutes; this is the beginning of the roux. Slowly begin adding the chicken stock, stirring continuously, until the mixture thickens. *Add the milk, slowly and stir until incorporated to the desired thickness.
Reduce the heat to a simmer and continue to cook for a further 10 to 12 minutes. Just before serving add the crabmeat and the peas and adjust the seasoning with salt and pepper, to taste. To serve, spoon into small bowls, sprinkle with chopped chives and top with a puff pastry disk.
*Cook's Note: By adding the liquid slowly it will help you see the desired thickness of the sauce. You may not need all of the milk, as some flours absorb different amounts of liquid. Just be careful.