Creamy Chicken Potpie Soup

• 1 sheet frozen puff pastry (from 1 [17.3-ounce] package), thawed
• 1 large egg
• 1/2 cup, plus 1 tablespoon, heavy whipping cream, divided

Flaky sea salt, to taste

• 3 tablespoons unsalted butter
• 1 medium yellow onion, chopped (about 1 1/2 cups)
• 1 cup thinly sliced carrots
• 1 cup thinly sliced celery
• 2 teaspoons finely chopped garlic
• 1 teaspoon chopped fresh thyme, plus more for garnish
• 1/4 cup all-purpose flour
• 1/3 cup dry white wine
• 4 cups chicken broth
• 1 1/2 cups (1/2-inch) diced peeled Yukon Gold potato
• 1 1/4 teaspoons kosher salt
• 1/2 teaspoon black pepper, plus more for garnish
• 2 cups packed shredded rotisserie chicken (about 12 ounces)
• 1/2 cup frozen green peas

1. Preheat oven to 400°F. Unfold puff pastry onto a clean work surface; cut puff pastry into 1-inch squares. Arrange squares in a single layer on a parchment paper-lined baking sheet. Freeze until firm, about 5 minutes. Whisk together egg and 1 tablespoon of the cream in a small bowl. Brush pastry squares lightly with egg wash; sprinkle evenly with flaky salt, to taste. Bake in preheated oven until deeply golden brown and puffed, 12 to 14 minutes. Transfer to a wire rack; let cool completely, about 10 minutes.
2. Meanwhile, melt butter in a large Dutch oven over medium. Add onion, carrots, and celery; cook, stirring often, until vegetables are softened but not browned, 8 to 10 minutes. Add garlic and thyme; cook, stirring often, until fragrant, about 30 seconds.
3. Sprinkle flour evenly over vegetable mixture; cook, stirring constantly, until mixture is lightly golden and smells toasted, about 2 minutes. Stir in wine, scraping up any browned bits from bottom of Dutch oven; cook, stirring constantly, until wine is mostly reduced and mixture is thickened, about 1 minute.
4. Gradually stir in chicken broth until smooth. Stir in potatoes, pepper and salt. Bring to a boil over medium-high; reduce heat to medium-low, cover and simmer, stirring occasionally, until potatoes are tender, 10 to 15 minutes.
5. Stir in shredded chicken, peas, and remaining 1/2 cup heavy cream. Cook over medium, uncovered, stirring occasionally, until chicken is heated through, about 5 minutes.
6. Ladle soup evenly into 4 to 6 bowls. Top generously with puff pastry croutons, and garnish with fresh thyme leaves and additional black pepper. Serve immediately.