1. Place potatoes in a saucepan; cover with water. Bring to a boil. Reduce heat; simmer for 5 minutes or until almost tender. Drain; rinse with cold water. Cut crosswise into thin slices.
2. Preheat oven to 400°.
3. Unfold dough; place on a surface dusted with flour. Roll to a 10 x 9inch rectangle. Cut into 20 (2 1/4 x 2inch rectangles). Score each rectangle about 1/8-inch from edge. Prick dough liberally with a fork. Arrange on a baking sheet lined with parchment paper; chill 10 minutes.
4. Arrange 2 potato slices onto each dough piece, and sprinkle with salt. Combine cheese and rosemary. Sprinkle about 3/4 teaspoon cheese mixture over each tartlet. Bake at 400° for 15 minutes or until golden.