Preheat your oven to 190°C (375°F). While it heats, prepare your mise en place: dice the onion into ½-inch pieces, chop the bacon into 1-inch strips, slice the mushrooms, peel and slice the carrots into ½-inch rounds, and slice the leek into ½-inch rounds (using both white and light green parts). This prep work takes just a few minutes and ensures everything is ready when you need it.

Pat the chicken thighs dry with paper towels, then season generously on both sides with salt and freshly ground black pepper. Heat the olive oil in a large oven-safe pan or Dutch oven over medium-high heat until shimmering. Working in batches if needed to avoid crowding, place the chicken skin-side down and cook for 7-8 minutes until the skin is golden and crispy. Flip and cook the other side for 3 minutes, then transfer to a plate. I like to let the skin get really golden here because it adds wonderful flavor and texture to the finished dish.

In the same pan with the rendered chicken fat, add the chopped bacon and cook for 2-3 minutes until the fat renders and the bacon begins to crisp. Add the diced onion and cook for 2 minutes, stirring occasionally. Then add the sliced mushrooms and cook for another 2 minutes until they begin to soften. This layering of flavors—bacon first, then aromatics, then mushrooms—ensures each ingredient contributes its best to the sauce base.

Add the sliced carrots to the pan and stir for 1 minute to combine with the aromatics. Sprinkle the flour over everything and stir well for about 1 minute—this coats the vegetables and begins to thicken the sauce. Add the dried thyme and bay leaf, then pour in the chicken stock while stirring constantly to prevent lumps from forming. Bring the mixture to a gentle simmer.

Return the seared chicken thighs to the pan, nestling them skin-side up into the sauce. The chicken should be mostly submerged but the skin should peek above the liquid to stay crispy. Cover the pan with a lid or aluminum foil and transfer to the preheated 190°C oven. Bake for 45 minutes—during this time the chicken will cook through, the flavors will meld, and the sauce will thicken slightly.

Remove the pan from the oven and carefully stir in the sliced leeks, distributing them evenly throughout the casserole. I like to add the leeks at the end rather than with the other vegetables because they're delicate and cook quickly—this keeps them from becoming mushy. Return the pan to the oven, uncovered, and bake for a final 15 minutes until the leeks are tender and the sauce has reduced slightly.

Remove the casserole from the oven and let it rest for 5 minutes before serving. This allows the flavors to settle and makes plating easier. Taste and adjust seasoning with additional salt and pepper if needed, then serve hot directly from the pan or in shallow bowls, ensuring each portion has a chicken thigh, vegetables, and plenty of sauce.