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.
Preheat oven to 400 degrees. Unfold dough; place on a surface dusted with flour. Roll to a 10x9 inch rectangle. Cut into 20 (2 1/4 x 2 inch) rectangles. Score each rectangle about 1/8 inch from the edge. Prick dough liberally with a fork. Arrange on a baking sheet lined with parchment paper; chill 10 minutes.
Arrange 2 potato slices onto each dough piece, and sprinkle with salt. Combine cheese and rosemary. Sprinkle about 3/4 teaspoons mixture over each tartlet. Bake at 400 degrees for 15 minutes or until golden brown.