In a large pot, melt butter over medium high heat. Add onions, celery, and broccoli and cook until softened about 3-5 minutes. Sprinkle with flour and cook an additional minute, stirring constantly. Slowly add broth, milk, cream, red pepper flakes, salt, and pepper. Use a whisk to combine, then add cooked chicken. Heat until warm, about 10-15 minutes.

To make crust strips, unroll thawed pie crust. Cut into strips and lay on parchment-lined baking sheet. Bake in a 450°F oven for 6-8 minutes until browned. Remove from oven.

To assemble, pour soup into individual bowls, top with shredded cheese and pieces of pie crust strips. Serve immediately.