In a large saucepan, bring water (or broth) to boil; add cornmeal and salt; reduce heat to medium
Using a wooden or metal spoon, begin to stir the mixture; it will spit and spatter, so be careful; continue to stir until mixture begins to thicken and pull-away from the sides of the saucepan; you may have to reduce the heat a bit here!
Remove from heat; taste for salt; add butter (optional); add any spices or seasonings now
Pour contents into non-stick (or lightly oiled) muffin pan; place muffin pan in fridge for about 15 minutes
Preheat oven to 350ºF; adjust cooking rack to the middle
Remove muffin pan from fridge and, using wet fingers or the back of a wet spoon, begin to massage the cornmeal into cups
Once cups are formed, bake for 25-30 minutes on middle rack
NOTE: the color of the polenta will not change; to test for doneness, gently push on the bottom of the cup; it should be relatively firm
Once cups are baked, remove muffin pan from oven and allow to cool for about 10 minutes;
Use a knife to score the perimeter of each muffin pan, gently loosening the cup
Place polenta cups on wire rack to cool
If serving immediately, place cups on serving platter and fill with contents
If you're making the polenta cups in advance, store in a air-tight container in the fridge for up to three days;
When it's time to serve the cups, simply pop them on a baking sheet and re-heat until warm throughout; plate, fill and serve