Heat the butter and olive oil in a large pan over medium heat. Once melted and slightly bubbling, add the diced chicken. Let it cook until lightly golden on the outside. You don’t need to cook it fully at this stage—it will finish cooking later in the sauce and oven. Remove the chicken and set aside.

In the same pan, add your sliced leeks. Cook them gently over medium-low heat for about 5–7 minutes. Stir occasionally and let them soften slowly. This step is important—the slower you cook the leeks, the sweeter and more delicate their flavor becomes.

Add the garlic and cook for another minute, just until fragrant.

Sprinkle the flour over the leeks and stir well so everything is coated evenly. Cook this mixture for about a minute to remove the raw flour taste.

Now slowly pour in the chicken stock, stirring constantly to keep the sauce smooth. Once combined, add the double cream and Dijon mustard. You’ll notice the sauce becoming rich and silky.

Return the chicken to the pan. Add thyme, salt, and black pepper. Let everything simmer gently for 8–10 minutes until the chicken is fully cooked and the sauce has thickened beautifully.

At this point, taste your filling. Adjust seasoning if needed—this is where you can make the dish truly yours.

Transfer the filling into your pie dish. Let it cool slightly—this helps prevent the pastry from becoming soggy.

Place the puff pastry over the top, trimming any excess. Press the edges down to seal.

Brush the pastry with beaten egg for that glossy, golden finish. Cut a small slit in the center to allow steam to escape.

Bake in a preheated oven at 200°C (180°C fan) for 20–25 minutes, or until the pastry is puffed and beautifully golden.

Allow the pie to rest for about 5 minutes before serving. This small step makes a big difference—it helps the filling settle and makes slicing easier.