Bring 4 cups water to a boil in a medium saucepan. Gradually add polenta and salt, stirring constantly with a whisk. Reduce heat to low, and cook for 4 minutes or until thick, stirring frequently. Stir in butter. Spoon polenta into a 9-inch square baking pan coated with cooking spray, spreading evenly. Press plastic wrap directly onto surface of polenta; chill for 1 hour or until polenta is very firm.
Cut into 30 squares.
Combine 1/4 cup boiling water and currants in a small bowl.
Let stand for 10 minutes or until currants are plump; drain.
Combine currants, cheese, pine nuts, and orange rind in a small bowl.
Heat vinegar in a small saucepan, and cook over medium-low heat until reduced to 2 tablespoons (about 10 minutes). Cool slightly.
Heat a large nonstick skillet over medium-high heat. Coat the pan with cooking spray.
Add half of polenta squares to pan, and cook for 6 minutes on each side or until golden.
Remove polenta squares from pan, and keep warm. Repeat procedure with the remaining polenta. Top each square with rounded 1/2 teaspoon of cheese mixture, and drizzle with about 1/4 teaspoon balsamic vinegar.
