Preheat and prep - Preheat oven to 375°F (190°C) and lightly grease a casserole dish with butter.
Prepare the chicken - Season bite-sized chicken pieces with salt, pepper, and garlic powder.
Sauté aromatics - Melt butter in a pan and sauté onion and garlic until soft and fragrant.
Make the creamy sauce - Add heavy cream and chicken broth, stir until slightly thickened. Adjust seasoning to taste.
Combine ingredients - Add chicken and frozen vegetable mix to the sauce, stirring until everything is evenly coated. Transfer to prepared casserole dish.
Top with biscuits and cheese - Arrange cheddar bay-style biscuits on top and sprinkle with extra shredded cheese if desired.
Bake - Bake for 25-30 minutes until biscuits are golden brown and casserole is bubbly. Let rest for 5 minutes before serving.