Preheat the oven to 180°C (350°F).

Season the chicken thighs with salt and pepper. Heat olive oil in a large oven-safe skillet over medium-high heat. Brown the chicken thighs on both sides, then remove and set aside.

In the same skillet, add the chopped onion and garlic. Sauté for 2-3 minutes until fragrant.

Add the wine (or chicken stock) to deglaze the pan, scraping any brown bits off the bottom. Stir in the butter and allow it to melt.

Sprinkle in the flour and cook, stirring constantly for 1-2 minutes.

Slowly whisk in the chicken stock, Dijon mustard, and cream. Bring to a simmer and cook for 3-4 minutes until the sauce thickens.

Return the chicken thighs to the skillet, skin-side up. Add thyme sprigs or dried thyme, then transfer the skillet to the oven.

Bake for 35-40 minutes, or until the chicken is cooked through and the internal temperature reaches 75°C (165°F).

Remove from the oven and sprinkle with grated parmesan. Return to the oven for an additional 3-5 minutes until the cheese is melted and bubbly.

Serve the chicken with mashed potatoes and steamed greens or a leafy green salad. Garnish with fresh thyme leaves, if desired.