Prepare the flowers Gently shake the dandelion heads to remove any insects, then pull away as much of the green base as you reasonably can, keeping mostly the yellow flower parts.
Make the infusion Place the prepared dandelion flowers in a large saucepan with the water, sliced lemon and split vanilla pod. Bring gently to a simmer and cook for around 20–30 minutes.
Leave to steep Remove from the heat, cover and leave to steep for several hours or overnight.
Strain Strain the mixture through a fine sieve, muslin or clean cloth, pressing gently to extract as much liquid as possible. Discard the spent flowers and lemon.
Add the sugar Return the strained liquid to the saucepan. Add 800g sugar to begin with and heat gently, stirring until completely dissolved. Add more sugar, up to 1kg, if you prefer a sweeter or thicker syrup.
Reduce the syrup Bring to a gentle simmer and allow the mixture to reduce slowly until it begins to thicken and takes on a deep golden colour.
Check the consistency Spoon a small amount onto a chilled plate and leave it for a minute. You are looking for a runny honey consistency. Remember that it will thicken further as it cools.
Jar the dandelion honey Carefully pour the hot syrup into clean, sterilised jars or bottles. Seal and allow to cool before storing. Store