Preheat the oven to 220 °C/Fan 200°C /Gas 6.
Place the pheasant and all the stock ingredients in a pot and add enough water to submerge everything. Bring to the boil.
Simmer for 30 minutes then check the pheasant is cooked by piercing the inside of the leg to see if the juices run clear (alternatively, you could use a meat thermometer). When they do, turn off the heat and leave the pheasant to sit in the stock for 10 minutes.
Remove the pheasant and let it cool.
Drain out the vegetables and reserve the stock for use in the sauce.
When the pheasant is cool enough, remove the meat and shred the wild bird using two forks to pull the meat in opposite directions. Set aside.
Bubble the stock until it has reduced to 700ml. Heat some vegetable oil and cook the bacon in it until it is starting to crisp. Add the onion, cook till soft. Add the butter, garlic and herbs. When all the butter has melted, add the 2 tbsp flour.
Add the stock gradually, stirring vigorously between additions, until you have a glossy sauce. Season with salt and pepper if needed, then switch the heat off and stir in the cream.
In a food processor, whizz the flour and bread until you have a breadcrumb-like mixture. Add the Parmesan and whizz until combined. Add the butter and whizz until the mixture looks like breadcrumbs again.
Place the pheasant, sweet potatoes and sauce in a baking tin, lasagne dish or similar. Top with the crumble and cook in the preheated oven for 30 minutes until golden brown.