1. Heat olive oil in a large, deep skillet over medium-high heat. Season the chicken thighs with salt and pepper.
2. Add the chicken to the skillet, skin-side down, and cook until the skin is golden brown and crispy, about 5-7 minutes. Flip and cook for another 5 minutes. Remove chicken and set aside.
3. In the same skillet, add diced onion and cook until translucent, about 3 minutes, scraping up any brown bits from the bottom of the pan. Stir in the minced garlic and cook for another minute until fragrant.
4. Pour in the chicken broth, heavy cream, and Dijon mustard. Stir well to combine and let it simmer for 5 minutes, allowing the sauce to thicken slightly.
5. Return the chicken thighs to the skillet, skin-side up. Sprinkle with thyme and Parmesan cheese. Cover and simmer for 15 minutes, or until the chicken is cooked through.
6. Stir in the baby spinach and let it wilt into the sauce. Taste and adjust seasoning if necessary.
7. Remove from heat and let the dish rest for a few minutes before serving.

One tip I’ve learned from my grandmother is to always taste as you cook. This way, you can adjust the seasoning to your liking, ensuring every bite is just as flavorful as you want it to be.