Put the almonds, milk and bay leaves into a pan and heat gently until steaming and almost bubbling. Remove from the heat and leave to infuse for 30 minutes.
Strain the milk through a fine sieve into a large jug. Discard the bay leaves, and spread the almonds on kitchen paper to dry.
Heat the plain flour and butter in a large pan and stir until melted to a smooth paste. Cook for a couple of minutes, then gradually stir in the milk until you have a smooth sauce. Keep stirring until the sauce thickens and comes to a gentle bubble. Turn off the heat and stir in the cheese. Season with the nutmeg and some salt and pepper.
Bring a large pan of water to the boil. Add 2-3 cauliflowers at a time, and boil each for 3 minutes, then drain.
Put the almonds, bread, garlic, olive oil and sage into a food processor and pulse to make chunky crumbs.
Space the baby cauliflowers in a deep oven tray, then pour over the manchego sauce. Scatter the nutty crumbs over and dot with a few extra knobs of butter.
Heat the oven to 200C/fan 180C/gas 6, then bake the gratin on a high shelf for 20-25 minutes until the cauliflowers are tender, crumbs golden and sauce bubbling.