Preheat oven according to package directions for puff pastry shells. Arrange shells on a non-stick baking sheet then place in oven. Bake until golden, remove from oven and let cool.
Place a large deep-sided skillet over medium-high heat with 2 turns of the pan of EVOO, about 2 tablespoons. Add celery, onions, carrots, bay leaf and season with a little salt and pepper.
Cook, stirring frequently, for about 5 minutes, until the veggies start to get tender. Add the red bell pepper and continue to cook for an additional 2-3 minutes. Scoot the veggies over to the sides and add the butter to the center of the skillet. Once butter has melted, add flour and cook for about a minute.
Whisk in white wine, chicken stock and cream. Bring the liquids up to a simmer then add the chicken pieces. Bring back up to a simmer and add the asparagus. Simmer mixture until the chicken is cooked through and the asparagus is tender, about 10-12 minutes.
Add peas and tarragon and stir to combine. Taste and add salt and pepper to taste.
To serve, place 2 shells on each dinner plate and fill each shell with the chicken mixture. Replace pastry lid and top with a sprig of tarragon.