- Make the dough: Combine flour, polenta or cornmeal, baking powder, salt, and rosemary in a small bowl; set aside. Cream together sugar and butter until smooth. Add egg and yolk; beat until incorporated. Add dry mixture and mix until dough forms—it should be cookie-like and malleable. Transfer 1/3 of dough to a lightly floured work surface and roll into a log. Wrap in plastic and place in freezer. Press remaining dough evenly into a springform or 9-inch tart pan with a removable bottom. Press dough up sides of rim. Set on a baking sheet and freeze until thoroughly chilled.
- Make the jam: Combine all ingredients in a medium saucepan, making sure to have enough space for jam to boil and rise. Cook over medium heat until boiling, about 10 minutes. Skim surface of foam if needed. Jam will reduce slightly. Test for doneness with plate test—place a plate in freezer; once cold, put a teaspoon of jam on plate. Jam should gel and set without moving. If it does not, cook 5 more minutes and test again. Let cool completely before assembling tart.
- To bake, preheat oven to 375 degrees. Spread jam evenly over unbaked tart shell. Slice dough log into disks, about 1/3-inch thick. Lay over jam, covering top. A few open spots are okay. At this point, wrap and freeze assembled tart for up to 2 weeks; thaw overnight in refrigerator before baking. Sprinkle raw sugar and chopped rosemary over crust and bake for 25 to 30 minutes, until golden brown. Let cool before removing from pan.