In a large bowl, beat sour cream, eggs, oil, lemon peel, and lemon juice until well blended. In another bowl, stir together flour, polenta, baking powder, and 1/2 cup sugar. Stir or beat into sour cream mixture until well blended.
Pour mixture into an oiled 9-inch fluted tart pan with a removable rim. Sprinkle pine nuts and remaining 1/4 cup sugar evenly over the top.
Bake in a 350° oven until golden brown, about 35 minutes. Let cool about 30 minutes, then remove pan rim. Serve warm or cool, cut into wedges.