Preheat an oven to 180°c/160°c fan (356°f/320°f).
Lightly trim the tops off each bulb of garlic, to expose the cloves then place each bulb onto its' own sheet of foil. Drizzle the garlic with olive oil, season with salt & pepper then roast in the preheated oven for 45 minutes - 1 hour, until the cloves are golden brown & soft. Once cooked, let the garlic cool whilst you make the bechamel.
Next, add the butter into a large saucepan, set over a medium heat, cook until melted then stir in the flour & cook out for 1 minute.
Pour a third of the milk into the roux, whisk until smooth then cook out until thick, stirring/whisking regularly. This will take 2-3 minutes over a medium heat.
Once thick, pour half of the remaining milk into the pan then continue cooking until thickened again. Repeat this process with the rest of the milk, making sure to whisk/stir the sauce frequently to keep it from catching on the bottom of the pan.
Next, stir the chicken stock into the bechamel then turn the heat down to low & cook until the sauce has thickened for a final time. If you give it a taste, it should taste cooked out, not like flour!The bechamel should be thick enough to coat the back of a spoon once cooked. Once the sauce is cooked, turn the heat down to low, stir in the grated parmesan, to melt then add in grated nutmeg, to taste. Season the bechamel with salt & pepper then take the pan off the heat.
Next, squeeze the roasted garlic out of the skins then use a stick blender to blend roasted cloves into the sauce then set to one side. You can add as much of the roasted garlic into the bechamel as you like!If you haven't got a stick blender, use a jug blender instead! I'd recommend adding at least a bulb of garlic into the sauce but feel free to make it as garlicky as you like.