Mashed Potatoes:

1. Place the potatoes in a large pot and cover with water. Bring to a boil and cook until tender when pierced with a fork, about 15-20 minutes.

2. Drain the potatoes and return them to the pot. Add butter, heavy cream, and salt. Mash with a potato masher or electric mixer until smooth and creamy. Keep covered and warm.

Chicken:
3. Preheat oven to 375°F.
4. Season chicken breasts on both sides with salt, pepper, and garlic powder.
5. Heat butter and olive oil in an oven-safe skillet over medium-high heat. Once hot, add chicken and cook for about 5 minutes on each side until browned. Remove chicken to a plate.

Dijon Cream Sauce:
6. Reduce heat to medium. In the same skillet, melt butter and sauté minced garlic until fragrant.
7. Whisk in flour and cook for 1 minute to form a roux.
8. Gradually whisk in ½ cup chicken broth, stirring to prevent lumps.
9. Add Dijon mustard, salt, pepper, and remaining ½ cup chicken broth. Stir well.
10. Pour in heavy cream and simmer for 1-2 minutes until sauce thickens slightly.

Bake and Serve:
11. Return chicken breasts to the skillet, spoon some sauce over them, and transfer the skillet to the oven. Bake for 15-18 minutes, or until chicken is cooked through (internal temperature of 165°F).
12. Serve the chicken and creamy Dijon sauce over mashed potatoes. Garnish with chopped parsley if desired.