Place a large pot over medium high heat (closer to high heat). Place the butter in the pot to melt it.
Put the chopped onions into the butter and cook for 3 minutes to make the onions translucent.
Sprinkle in the flour and stir everything together so all of the flour is combined with the butter and onions.
Pour in the chicken broth and whisk together until all of the flour has dissolved in the broth.
Add the heavy cream, pepper and salt to the pot and stir together. Let the pot come to a bubble (about 5 minutes).
Add the frozen veggies and shredded chicken to the pot and stir together. Let cook together for 2 more minutes.
Pour all of the contents of the pot into a large casserole dish. Open the can of biscuit dough and place the individual biscuits on top of the contents about 1-2 inches apart.
Place the dish in the oven to bake for 20 minutes.