Pluck the parsley from the stems and fry them in oil in a pan until crispy. Then drain on kitchen paper.
Peel the celery and cut into large cubes. Immediately cover with water, season with 1 tablespoon of lemon juice and salt and cook for 20 minutes until soft. Line a sieve with a cheesecloth or a strainer cloth. Drain the celery through the cloth and squeeze it out well with a trowel.
Cut the cold butter into cubes and place in a food processor with the celery. Season with salt, pepper, nutmeg and the remaining lemon juice and mix for 2-4 minutes. Garnish with the parsley and lemon wedges.