Chicken Mushroom Pie with Duchess Potato lid

Bahan-bahan (6 porsi)

• 60 g / (4 tbsp) unsalted butter (, approximately divided into 4 (no need to be accurate))
• 4 g arlic cloves (, finely minced)
• 1 1/2 tsp cooking salt / kosher salt (, divided (Note 1))
• 1 tsp black pepper (, divided)
• 750 g / 1.5 lb chicken thighs (, boneless skinless (Note 2))
• 500 g /1 lb button mushrooms - very small ones whole (, larger ones halved or quartered)
• 100 g / 3.5 oz thick cut streaky bacon (, cut into 2.5cm/1" squares)
• 1 1/2 onions (, cut into 2cm/1" square or thick wedges)
• 2 sprigs fresh thyme ((or 1/2 tsp dried thyme))
• 1/4 cup plain flour ((all-purpose flour))
• 3/4 cup Guinness beer ((Note 3))
• 1 1/2 cups beef stock / broth (, low sodium)
• 3/4 cup water
• 1 tbsp tomato paste
• 1 kg / 2 lb starchy potatoes (, peeled, cut into 2.5cm / 1" cubes (Note 4))
• 30 g / 2 tbsp unsalted butter (, cut into 1.5 cm / 1/2" pieces)
• 1/3 cup milk (, hot)
• 1/8 tsp white pepper ((sub black))
• 30 g / 2 tbsp unsalted butter (, melted (or olive oil spray))
• 2 tbsp grated parmesan (, sandy store bought type works best or grate your own)
• 2 tsp finely chopped parsley for garnish (, optional)