Tip:For the neatest servings, let the gratin sit for at least 10 min. before slicing.
Heat the oven to 375°F. Rinse a small saucepan in cold water (this will make the pan easier to clean later), add-the cream, garlic, bay leaf, thyme, and nutmeg. Bring to just below a simmer over medium heat, remove from the heat, cover, and set aside to infuse for about 30 min.
Brush a large gratin dish or 3-qt. flameproof casserole dish with a little of the melted butter. Arrange half of the rutabaga slices in the bottom of the dish, followed by half of the potato slices. Season with salt and pepper. Dot the surface with the blue cheese. Continue with another layer of rutabaga slices and a final layer of potatoes. Season the top with salt and pepper. Strain the seasoned cream over the top. In a small bowl, combine the breadcrumbs with the remaining melted butter and sprinkle over the top. Butter the dull side of a large sheet of foil and cover the gratin. Bake for 40 min., remove the foil, and continue to bake until the top is browned, the sides are bubbly, and the potatoes are tender when pierced, another 30 to 40 min. Let sit for 10 min. before serving.