Clean, slice and put the head of celery in a pot with a little water. Cover and simmer until it softens, probably an hour. Crush the celery into a sieve to extract the maximum juice, then strain the liquid through muslin to remove any bits. You want this as clear as possible.
Reduce the liquor to 2/3 cup, add Ricard to taste.
Allow to cool, then sprinkle a scant teaspoon of agar flakes onto the surface,
slowly bring to a simmer, then simmer and whisk until the flakes have dissolved. You may need to add a little more water to absorb all the agar lumps. You may also need to boil quite hard.
Pour into a mould and chill

Peel and dice the beetroots, put in a pot with a little water. Cover and simmer until softened, probably one hour. Strain the beetroot through a sieve, crushing out any extra juice. If you don't crush too hard you won't have bits that need to be strained out.
Reduce the liquor to 2/3 cup, add balsamic vinegar to taste. You want a slight edge of acid tartness, but don't drown the nice round earthy flavour of the beetroot. Allow to cool, then sprinkle a scant teaspoon of agar flakes onto the surface,
slowly bring to a simmer, then simmer and whisk until the flakes have dissolved. You may need to add a little more water to absorb all the agar lumps. You may also need to boil quite hard.
Pour into a mould and chill