Cook 3 slices chopped bacon in a saucepan until crisp. Remove; discard all but 2 tablespoons drippings. Add 1 chopped small onion and 1 minced garlic clove,; cook 3 minutes. Sprinkle in 1 tablespoon flour; cook, stirring, 1 minute. Whisk in 1 1/2 cups milk,; season with salt and nutmeg,. Cook until thickened, 4 minutes. Stir in 1/2 cup shredded gruyere,, 1 pound thawed frozen chopped spinach, (squeezed dry) and the bacon. Cook 2 minutes.