Preheat oven to 375ºF.
Place a large saucepot over medium-heat and melt the butter. Add garlic to pan and cook until aromatic, about 1 minute. Sprinkle the flour over the butter and garlic, and cook for about 1 minute. Whisk the milk into the butter-flour mixture and bring up to a bubble. Add the nutmeg, season with salt and ground black pepper, and simmer until thickened, 3-4 minutes.