The name “Imbolc” comes from Celtic origin: oimelc means “ewe’s milk,” after the lactating sheep that have given birth to their lambs. This is also the time of a dwindling food supply. Stored root vegetables from last autumn, along with fresh milk and lamb, are the main staples during this time of year in the northern climates. That is why these foods are typically used for an imbolc celebration.   Any root vegetable will work in a gratin. Try potatoes, sweet potatoes, carrots, parsnips, and even winter squash. Gratins aren’t picky. You really don’t need a recipe. Just make sure to thinly slice your onions and root vegetables. Use fresh cream or raw milk. Sometimes I sprinkle the top with almond flour when I…