Heat the olive oil in a large heavy-based ovenproof pot over medium-high heat. Add the bacon and cook for 3–4 minutes until lightly golden. 

Add the leek and onion. Cook for 10 minutes, stirring often, until soft. 

Add the garlic and thyme and cook for 1–2 minutes until fragrant. 

Add the butter and celery and cook for 4 minutes, stirring occasionally. 

Add the chicken and cook for 5–6 minutes until lightly coloured. 

Sprinkle over the flour, mix through and cook for 2 minutes. 

Pour in the beer or wine and let it reduce for 3 minutes. 

Slowly pour in the chicken stock while constantly stirring to avoid lumps. Bring to a simmer. 

Stir through the mustards and thickened cream. Season to taste with salt and pepper and let cook for 15 minutes until the sauce is thick and coats the back of a spoon. 

Preheat the oven to 180°C (160°C fan-forced). 

In a baking dish, spread a thin layer of the chicken mixture. Top with fresh lasagna sheets, then add a thicker layer of chicken mix and a sprinkle of cheese. Repeat layers, finishing with sauce and cheese on top. 

Bake for 35–40 minutes until golden and bubbling on top. Remove from the oven and rest for 15 minutes before slicing and serving.