Finely grind the mushrooms using a food processor, chop the onion and finely chop the parsley and carrot.
Fry the onion and carrot in a skillet with some oil and add the mushrooms. let it cook for a minute while stirring, add the wine and let the mixture reduce until the moisture is almost gone.
Add the cream to the skillet and let it reduce to a thick, spreadable mixture. Stir in the parsley and season with salt, pepper and lemon zest. Remove from the pan and let cool. Peel the celeriac and cut off 4 slices of about 3 mm. Cut them to the same size as the 'burger', fry them in a little bit of oil for a few minutes and let them cool.
Briefly fry the burgers in some oil over high heat until they are slightly brown. Remove from the pan and let them cool. Preheat the oven to 200℃ and let the slices of dough thaw.
Roll out the pie dough slices one at a time to about half as large the the size of the original slice. Place a slice of celeriac in the middle, sprinkle with breadcrumbs and place a burger on top.
Spread a layer of 'duxelle' (mushroom mixture) on the burger. Brush the edges of the dough with some water and fold the ends towards each other over the filling. Pinch the seams closed and place the parcel on baking paper on a baking tray. Cut stars from the 2 extra dough slices.
Brush all the parcels and stars with a beaten egg or some water and sprinkle with sesame seeds. Bake them for about 10 minutes on a baking tray with baking paper until golden brown.
For the sauce: fry a finely chopped shallot in the butter until translucent and add the mushrooms (coarsely chopped). Stir in the flour and let it cook for a while. Deglaze with the red wine and let it boil for a while. Add the stock, bring to a boil and simmer for a few minutes. Cut 1 cm from the bottom of the asparagus and cook them until crispy (about 4 minutes). Drain and season with salt and pepper. Serve the wellingtons with the sauce, asparagus and stars.