Begin by preparing the choux pastry. Place the water, salt, sugar and butter in a small pan and bring to the boil. Remove from the heat, then add the flour and mix well with a wooden spoon

Return to a low heat and mix well for 45 seconds to dry the mix slightly. Remove from the heat again and mix in the eggs one by one, stirring well with a spoon after each addition. Once the eggs are incorporated, set aside to cool

Meanwhile, prepare the filling. Melt the butter in a small saucepan until foaming and golden brown, then add the flour. Stir well with a wooden spoon, pour in the milk and mix well with a whisk to remove any lumps. Season, add the grated cheddar, then taste and season to taste. Set aside

Preheat the oven to 170°C/gas mark 3.5

Transfer the choux mixture to a piping bag and pipe balls of pastry onto a baking sheet lined with greaseproof paper, approximately the size of large olives. Repeat until all of the mixture is used up

Dip a pastry brush in a little milk and very lightly brush the top of each choux bun, gently pushing down the soft peaks

Sprinkle the top of the buns with a little Parmesan, then bake in the oven for approximately 10 minutes, or until golden brown and dried on the outside

Heat a dash of olive oil in a frying pan over a medium heat. Once the oil is hot, cook the mushrooms for 5-6 minutes until all the moisture has been released. Lower the heat, add the garlic and cook out for 1-2 minutes. Finish with the parsley and tarragon, then remove from the heat and chop the mixture very finely on a chopping board

Stir the mushrooms through the cheese sauce, add the truffle oil and place in a piping bag with a small cut at the end. Fill each of the choux buns, then dip the top of each bun in the cep powder to lightly coat. Arrange the buns on a platter decorated with mushrooms and serve