Creamy Braised White Beans

unsalted butter

head garlic, halved crosswise

whole milk

chickpeas, with their liquid

white beans, such as cannellini or Great Northern, drained and rinsed

thyme sprig, 2 sage leaves or 1 bay leaf

ground nutmeg, allspice or garam masala

Kosher salt and black pepper

slices crusty bread or thick toast

Extra-virgin olive oil, for serving

Freshly grated Parmesan, for serving

Aleppo pepper or red-pepper flakes, for serving