Preheat a pan to medium-high heat.
Add about a teaspoon of butter and a teaspoon of olive oil and add enough chicken thighs to cover the base of the pan; don't overcrowd it. Let it sear on that side without moving it around for 2-3 minutes. Flip and repeat.
Remove the thighs from the pan and into the baking dish where they'll be going into the oven. Repeat with the rest of the chicken thighs.
In the same pan, add the onion, lemon zest and rosemary and sautée for 3-4 minutes over medium heat. If needed, add more fat.
Add the garlic and stir for a minute to cook.
Add the white wine and let it reduce until it thickens slightly. Season with salt and pepper.
Pour the sauce over the chicken and bake at 180℃/350℉ for 30-40min or until the centre of the thighs reach 73℃/164℉.
Serve hot over rice, with a fresh salad or mashed potatoes.