Place milk, broth and stock powder in a large saucepan. Bring to a very gentle simmer over medium heat, add chicken, pepper, bay leaves and thyme.

Place lid on, simmer gently on medium low for 15 minutes (do not boil, can make milk split).

Remove chicken and shred. Cover pot and set poaching liquid aside.

Heat half the oil and butter in a very large, deep skillet over high heat (or use large pot). Add half the mushrooms with half the garlic, salt and pepper.

Cook for 5 minutes, stirring leisurely, until golden. Transfer to bowl and repeat with remaining mushrooms.

Lower heat down to medium.

Melt butter in skillet, then add garlic. Stir until golden.

Add flour. Stir constantly for 1 minute.

Gradually pour in 2 cups of reserved poaching liquid while stirring constantly, it should turn into a thick paste.

Mix in another cup of liquid, then add remaining liquid and stir well to dissolve. Use whisk if necessary to make lump free.

Stir constantly for 1 to 2 minutes until it thickens - you should be able to draw a path across a spoon (see video).

Remove from heat, stir in cheese until melted. Taste and add more salt & peppers, if needed.

REMOVE 2 1/2 cups (625ml) of sauce (save for topping). Then stir in chicken and mushrooms into remaining sauce.

Preheat oven to 180°C/350°F.

Smear some sauce on the base of a 23 x 33 cm / 9 x 13" baking dish. Cover base with lasagna sheets.

Top with half chicken mixture, then lasagna sheets, remaining chicken mixture then more lasagna sheets.

Pour over reserved White Sauce, sprinkle with mozzarella. Cover loosely with foil or use upside down baking tray (ensure it's not touching cheese).

Bake for 25 minutes. Remove foil, bake further 10 minutes until golden and bubbly.

Stand 10 minutes, garnish with parsley if desired then cut to serve!