In a medium saucepan, melt 50 g (1¾ oz) of the unsalted butter. Add the eschallots, garlic and celery and sweat until translucent. Add the cauliflower florets and the chicken stock. Simmer on high heat until most of the liquid has been evaporated. Be careful not to allow the vegetables to colour when the liquid gets low. While the cauliflower is hot, put the solids and syrupy juices into an upright blender. Blend on high with the remaining unsalted butter until smooth. Pass through a fine drum sieve. Cover and refrigerate until required.