New Orleans Mac and Cheese

I'm always looking for a new way to do Mac and Cheese. I found a similar recipe for a skillet version but wanted to bump up the veggies and lower the fat. What came out of my oven was a rich cheesy mac and cheese with crisp veggies with an undertone of spice. I've been told that I'm making this again soon.

Serves 6-8
14oz chicken andouille sausage, sliced
28 oz can fire roasted diced tomatoes
2 1/2 cups chicken stock
2/3 cup SOS Mix
1 onion, diced
2 cloves garlic, minced
1 cup diced celery
16oz cooked elbow macaroni
2 cups shredded light cheddar cheese
1/2 cup shredded parmesan cheese
1 tsp dried thyme
Tabasco sauce
salt and pepper to taste
olive oil
cooking spray

SOS Mix
1 cup powdered milk
1 cup cornstarch
2 tbsp dehydrated onion flakes
Place all in a jar or zip lock bag, shake to combine
For every 1 1/4 cup liquid, whisk in 1/3 cup SOS mix, place over heat and season with salt and pepper. Cook over medium/high heat, stirring until thickened. Use in place of canned soup.

Preheat the oven to 350 degrees. Spray an oblong baking dish with the cooking spray and set aside. In a large skillet, heat 1 tbsp oil. Add the onion, celery, garlic. Season with salt and pepper. Cook until veggies begin to soften. Add the sausage, tomatoes and thyme. Cook until liquid from tomatoes has reduced. Set aside. In a small saucepan, whisk together the chicken stock and SOS Mix. Season with salt, pepper and tabasco. When the sauce has thickened, turn off the heat and add 1 1/2 cups of cheddar and all of the parmesan. Whisk until the cheese has melted. Mix together the sauce, cooked macaroni and veggies. Pour the mixture into the baking dish. Sprinkle remaining cheese over top and bake for 30 minutes or until the cheese has begun to brown and the dish is bubbly.