This savoury mille-feuille is layered with cheese, onion, grapes and scattered with roasted walnuts.
Preheat oven to 220C.
For the Quick Puff Pastry, place flour and 50g butter into a food processor and process until mixture resembles fine breadcrumbs. Add 120ml iced water and pulse until dough comes together in a ball, or add ½ teaspoon water at a time until a ball forms.
Press dough into a disc and wrap in cling wrap. Place the dough along with the remaining 200g butter into the freezer for 10 minutes.
Dust a clean work surface with flour. Unwrap dough and roll out into a rectangle 5mm thick. Grate 100g of the cold butter over the dough. Fold 1/3 of the rectangle inwards and fold the remaining 1/3 over the first fold to make 3 layers of dough. Turn the dough 90 degrees and roll out into a rectangle again, repeating the folding and turning once more. Wrap in cling film and place into the freezer for 10 minutes.
Roll pastry out as above and grate remaining butter over dough. Fold as above, turn 90 degrees, roll and fold again. Wrap in cling film and freeze for 10 minutes.
Dust the bench with flour. Remove the dough from the freezer, unwrap and roll out to a thickness of 3mm. Transfer dough to a lined tray and place into the freezer until firm.
Once dough is cold, cut into eight 5cm x 10cm rectangular pieces. Carefully lift the dough onto a baking tray lined with baking paper. Cover with a sheet of baking paper and another baking tray to keep pastry flat.
Cook in the oven for 10 minutes. Reduce the oven temperature to 180C and bake for a further 8-10 minutes, removing the top tray and baking paper for the last 2-3 minutes or until golden.
Remove from the oven and carefully transfer the cooked pastry to a tray and place into freezer to chill. Remove from the freezer and set aside in an airtight container until ready to assemble and serve.
For the Caramelised Onion, place shallots, butter and oil into a medium non stick saucepan over a medium heat. Cook, stirring, until soft and caramelised. Add the port and stir to deglaze the pan. Add sugar and salt and continue to cook for 1 minute. Stir in the vinegar then remove from the heat. Season to taste and set aside at room temperature.
For the Goats Cheese Mousse, place the ingredients into a bowl and process with a stick blender until fully combined. Season with salt to taste. Set aside in a piping bag in the fridge.
To serve, pipe 6 pillows of the Goats Cheese Mousse onto each plate, in a 5cm x 10cm rectangle. Top with the Caramelised Onion, crumbled Blue Stilton, chives, crumbled walnuts, sliced apple, sliced grapes and the celery heart leaves. Cover with a piece of pastry. Repeat filling layer as before, top with a piece of pastry and finish with a layer of filling.