Heat stock or water and salt in a pot and bring to low boil. Whisk in polenta and continue whisking for 3-5 minutes. Reduce heat a bit and cook 45 minutes or until very smooth and thickened.
Melt butter in small skillet. When it bubbles, add sage and cook to brown and crisp leaves. Remove sage to a paper towel-lined plate. Cook butter until it starts to brown and smelly nutty.