Cook the potatoes in a pan of boiling salted water for 10-15 minutes. Drain well, return to the pan and mash until smooth. Beat in 80g butter and the crème fraîche. Season generously.
For the filling, set a pan with the milk, fennel, bay leaf, cloves and peppercorns over a medium-high heat. Bring to the boil, then reduce the heat to medium. Poach the cod and prawns for 5 minutes. Remove with a slotted spoon and transfer to a plate. Strain the milk into a pan.
Set a large saucepan with the olive oil and remaining butter over a medium-high heat. Fry the turkey bacon for 6-8 minutes, until crisp and golden brown. Add the onion and leek and fry for 5 minutes more. Tip in the flour, stirring to coat. Slowly pour in the milk, whisking continuously. Bring to the boil, reduce to a simmer and cook for 5 minutes, or until thickened. Gently stir in the cod, prawns, peas and lemon zest. Season.
Preheat the oven to 180°C, gas mark 4. Divide the filling among four small baking dishes (or one large dish) and top with the mashed potato. Bake the pies for 20 minutes, or until the tops are golden. Serve with pea shoots.