Cut in half the garlic (horizontally), massage with olive oil and wrap in foil. Bake in a preheated oven at 190 for about 30 minutes until soft. Let it cool and squeeze the soft flesh into a bowl.
Peel the carrots, if needed, then chop up roughly. Put the chunks into a saucepan, cover with water and cook until tender. Drain.
Using a liquidizer, or a hand-held blender, process the carrot into a rough pulp. Add the lemon juice, roast garlic and butter then blend until you get a smooth purée. Season to taste and stir through.
Serve warm.