Skillet Chicken Pot Pie with Butternut Squash

Name: Skillet Chicken Pot Pie with Butternut Squash
Ingredients: ¼ cup olive oil; 1 cup frozen white pearl onions, thawed; 4 garlic cloves, finely chopped; 1 tablespoon chopped fresh sage; 1 small bunch kale, center ribs and stems removed, leaves chopped; Kosher salt, freshly ground pepper; ¼ cup all-purpose flour; 3 cups low-sodium chicken broth; ½ small butternut squash, peeled, cut into ½-inch pieces (about 1½ cups); ½ rotisserie chicken, meat torn into bite-size pieces (about 1½ cups); 1 sheet frozen puff pastry (such as Dufour or Pepperidge Farm), thawed; 1 large egg