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 chicken broth, milk, cream, red pepper flakes, salt, and pepper. Use a whisk to combine until smooth. Then, add in the cooked chicken. Heat over medium heat until warm and slightly thickened, about 10-15 minutes, stirring occasionally.

To make crust strips, unroll thawed pie crust (for one crust). Cut into strips and lay them on a parchment paper-lined baking sheet. Bake in a 450 degree F oven for 6-8 minutes, or until golden brown. Remove from oven.

To assemble, pour soup into individual bowls or ramekins. Top with shredded cheddar cheese and pieces of the baked pie crust strips. Serve immediately and enjoy!