Boil water or milk and salt in a medium saucepan over medium-high.
Gradually whisk polenta in a slow, steady stream, whisking constantly to prevent lumps.
Reduce heat to low; cook 15-20 minutes, stirring frequently with a wooden spoon, until thick, creamy, and pulling from pan sides.
Off heat, stir in butter, maple syrup, vanilla, and cinnamon until combined and butter melts.
Thin with a splash of milk or water if needed; polenta thickens as it cools.
Divide warm polenta among four bowls; add favorite toppings such as berries and honey.