Bring water and salt to a boil in a large saucepan. Add cornmeal, stirring constantly with a whisk until cornmeal begins to absorb liquid (about 2 minutes). Reduce heat to low; cook 20 minutes, stirring frequently. Stir in half-and-half; cook 15 minutes, stirring frequently.
Spoon cornmeal mixture into an 8-inch square baking dish coated with cooking spray. Using a spatula coated with cooking spray, spread into an even layer. Chill, uncovered, 30 minutes or until completely cool.
Preheat oven to 400°.
Turn polenta out onto dry surface; cut into 1/2-inch cubes. Place polenta cubes on a baking sheet coated with cooking spray. Bake at 400° for 45 minutes, turning once with a spatula. Cool on a wire rack.