Prepare the chicken by removing excess fat and cutting shallow slits into thick parts. Cut in half and season both sides with salt and pepper.

Mince the onion and garlic. Roughly chop the mushrooms and shiitake.

In a pan, melt butter over low heat. Add garlic and onion, sauté until onion becomes translucent. Add mushrooms and shiitake, stirring constantly to evaporate moisture for about 3 minutes.

Add flour to the pan and mix until no dry flour remains. Gradually add milk in portions, stirring until thickened. Season with salt and pepper to complete the mushroom sauce.

In a separate pan, heat salad oil over medium heat. Place chicken skin-side down and press with a spatula to ensure even browning. Remove excess fat with paper towels as needed. Flip and cook on low-medium heat for 3–4 minutes until fully cooked.