Chicken Pot Pie - Crumbled Topping

I originally found this on Cooking Classy, then discovered that was her adaptation of one on Cook's Illustrated. I don't have a subscription there and couldn't do a comparison. I found several other similar recipes, and adapted my own for our dinner tonight. I like it!! My notes in the recipe are in [brackets and italics]. I even remembered to take a picture - after we served ourselves, of course:

There are three separate segments in preparation:

The Filling:
2 large boneless skinless chicken breast halves (only I did one, plus two thighs)
1 14.5 oz can low-sodium chicken broth
1 Tbsp olive oil (only I used vegetable oil)
1 cup peeled and diced carrots (about 2 large carrots)
3/4 cup diced celery (about 2 large stalks)
3/4 cup finely diced yellow onion (about 1/2 medium onion)
1/2 cup finely sliced portabello mushrooms (optional) [Beloved Husband doesn't like these, so we added diced, slightly boiled, potatoes - adjust veggies for your family's tastes.]
2/3 cup frozen peas

The Sauce:
3 Tbsp butter
1/3 cup all-purpose flour
3/4 cup milk
1 tsp lemon juice
1 1/2 tsp dried parsley
1/4 tsp dried thyme
1 teaspoon soy sauce [Classy omitted this and the tomato paste - we included and it was good!]
1 teaspoon tomato paste

The Crumbles:
1 1/2 cups all-purpose flour
1 1/2 tsp baking powder
1/2 tsp salt
1/4 tsp freshly ground black pepper
1/4 tsp garlic granules (use 1/2 tsp if you prefer a slightly stronger garlic flavor)
1/4 cup butter, cold and diced into small cubes
2 oz. finely shredded Parmesan cheese (about 1/2 cup packed) (Didn't have any, so used a combination with Asiago)
3/4 cup + 2 Tbsp heavy cream

Now -- the putting it all together does work best in this order given by Classy:

1. Place chicken in a slow cooker, pour chicken broth over chicken. Cover with lid and cook on low heat about 5 - 6 hours until chicken is cooked through. [Of course, if you don't have that much time, do as I did and boil the chicken in the chicken broth while preparing the veggies.  Worked fine.]
2. Remove chicken, dice and set aside.
3. Strain broth from slow cooker through a fine mesh strainer into a bowl and reserve broth (if you don't have a fine mesh strainer just try to remove the pieces of fat).

Prepare the crumble:

1. Preheat oven to 450 degree.
2. In a mixing bowl, whisk together flour, baking powder, salt, pepper, garlic powder and optional cayenne pepper. [You know mine didn't have this pepper!]
3. Using your finger tips, cut butter into mixture until mixture resembles coarse crumbs.
4. Stir in Parmesan cheese.
5. Pour in heavy cream and mix just until combine.
6. Break and drop mixture into 1 - 2-inch pieces onto a Silpat lined baking dish. [I used our sheet cake pan and it worked just fine - nothing stuck. Silpat just isn't in my budget right now.]
7. Bake in preheated oven for 10 minutes until golden. Remove from oven and set aside.

Prepare the filling and sauce:

1. Heat olive oil over medium high heat. Once hot, add diced carrots, onion and celery.
2. Saute vegetables, stirring occasionally until lightly golden and tender, about 5 - 6 minutes.
3. Pour vegetables into a bowl and set aside.
4. Reduce heat to medium, melt butter in saucepan (I like to brown it a bit for and extra layer of flavor), then add in flour and cook, stirring constantly for about 20 seconds (it will be very thick).
5. While stirring, slowly add in milk followed by reserved chicken broth, lemon juice, tomato paste, soy sauce, parsley, thyme and season with salt and pepper to taste.
6. Bring mixture just to a boil, then slightly reduce heat and allow to cook about 1 minute longer until thickened, stirring constantly.
7. Remove sauce from heat and add sauteed vegetables, frozen peas and diced chicken to sauce, then toss to evenly coat. [Don't forget your choice of mushrooms or potatoes or ...]
8. Pour mixture into a 9-inch pie dish and sprinkle with baked crumble topping (Classy said hers: fit perfectly in my pie dish but if yours is coming close to the top edge you may want to sit it on top of a cookie sheet to prevent spills in your oven) [Mine had a few crumbles left over, so I treated myself to a taste before putting in the oven.]
9. Bake in 400 degree oven until nicely golden about 12 - 14 minutes. Serve warm.

It doesn't take nearly as long as it sounds, no 'processed' canned goods - all fresh ingredients (well, except for those frozen peas) - and it was very, very good. Add a salad, some fruit for dessert and you're done.