1-Preheat oven to 400°F (204°C): Arrange the broccoli and butternut squash in a single layer on a parchment-lined baking sheet. Drizzle with 1 tablespoon olive oil and season with salt and pepper, then roast for 20 minutes.

2-Meanwhile, heat the remaining 1 tablespoon olive oil in an oven-safe skillet over medium heat. Season chicken with salt and pepper, then cook for about 4 minutes per side until lightly browned but not fully cooked through. Remove the chicken and cover loosely with foil.

3-In the same skillet, melt butter, then add salt, pepper, onion, garlic, parsley, and chicken broth. Cook and stir for 5 minutes, scraping up any browned bits from the pan bottom to build that rich flavor.

4-Whisk cornstarch into half-and-half or whole milk, then slowly add this mixture to the skillet. Stir for about 1 minute until the sauce thickens into a creamy garlic base.

5-Return the chicken and roasted vegetables to the skillet, coating everything with the sauce. Transfer the skillet to the oven and bake for an additional 5 to 10 minutes, or until the chicken reaches 165°F (74°C).

6-Remove from the oven, garnish with fresh parsley if desired, and serve. This step ensures your garlic chicken and vegetables come out perfectly tender and flavorful.