For the tartlets: Make the polenta according to package instructions. Just before the polenta is finished thickening, add the cream, salt, and pepper. Pour the polenta onto a greased, rimmed baking sheet. Set aside to cool and firm up, about 30 minutes.
For the topping: In a medium bowl, combine the chicken, pesto, salt, and pepper. Stir to combine.
To assemble: Using a 2-inch diameter scalloped cookie cutter, cut the polenta into tartlet shapes, about 24, and place them on a serving platter. Top each polenta tartlet with a spoonful of chicken. Top the chicken with a few dried cranberries. Serve.