Bring a large pot of lightly salted water to a boil. Add rotini pasta and cook until al dente, 7 to 10 minutes. Drain, cover, and set aside until needed.

Melt butter in a saucepan over medium-high heat, and stir in 1 tablespoon olive oil. Add 1 cup broccoli; toss and cook until tender, about 5 minutes. Sprinkle broccoli with flour, and cook for 1 minute. Stir in the chicken broth, and bring to a boil. Pour in the milk and blend. Season with salt, pepper, and chipotle chile powder. Reduce heat to medium and simmer until sauce thickens, about 8 to 10 minutes. Mix in 1 cup Cheddar cheese and stir until melted. Remove from heat.

Heat the remaining 2 tablespoons olive oil in a skillet over medium-high heat. Stir in the onion, ground chicken, and 1 cup of broccoli. Cook until the chicken is browned and no longer pink, about 10 minutes. Season to taste with salt and pepper. Reduce heat, and cook until liquid is reduced, about 5 minutes.

Preheat oven broiler to high and lightly grease a 9x13-inch baking dish.

Toss the cooked pasta with the broccoli sauce until evenly blended. Stir in the sour cream, if desired. Combine the broccoli sauce mixture with the chicken mixture, and spoon into the prepared baking dish. Top with the remaining 1 cup of Cheddar cheese.