Separate the dill leaves from the stalks, and chop up the leaves (hold on to the stalks!).
Put the milk, onion, bay leaf and dill stalks into a medium-sized saucepan, and heat until it’s just about boiling.
Take off the heat and leave the mixture to infuse for 25 minutes, then strain it through a sieve (or take the bits out with a slotted spoon). Make sure the strained milk is nearby, as you add it in later.
Melt the butter in a non-stick pan, and stir in the flour – this will turn into a paste (known as a roux).
Cook this gently over a low heat for 3-4 minutes – and don’t stop stirring!
Now add in some of the strained milk and keep stirring until smooth. Continue to add in more milk until the sauce has thickened.
Simmer the sauce very gently for 10-15 minutes.
Add the chopped dill leaves and the lemon juice. Try a little bit (mind the heat), then add some ground black pepper to season it.
Top each dish with a bit of fresh dill to make it look extra-professional.