Next level cheese, potato and onion pie

Name: Next level cheese, potato and onion pie
Prep time: 40 min
Cook time: 1 h
Total time: 1 h 40 min
Cuisine: European
Ingredients: 250g plain flour plus extra for dusting; 50g rye flour (or make up the weight with plain flour); large pinch of cayenne pepper; 1tsp onion seeds; 25g parmesan or vegetarian alternative, finely grated; 125g cold butter cubed; 1 egg beaten; 40g butter; 3 large onions finely sliced; 2 bay leaves; 1tbsp thyme leaves; 1 medium potato (about 350g), halved lengthways and sliced; 100ml double cream; 150g extra mature cheddar ½ grated, ½ chopped into small chunks