Preheat oven to 350 degrees F. Grease a 9" tart pan (the kind where the bottom comes out). Set aside.
Combine flour, confectioners' sugar, and salt. Set aside. Melt butter and vanilla extract in a small bowl in the microwave in 30 second increments until melted. Stir butter into flour mixture with a spoon until all incorporated. Press mixture into the sides of the pan with your fingers then work your way to the middle, using a measuring cup to gently press down on crust to make sure crust is flat. Bake for 20 minutes or until crust is just barely golden. Let cool.
While the crust bakes and cools, make the cranberry curd: Place cranberries, sugar, rosemary, and orange juice and zest in a medium-sized saucepan over medium heat. Simmer until cranberries have popped and become tender, about 10 minutes. Remove sprigs of rosemary from the cranberries (it's okay if some of the leaves have fallen). Transfer mixture to a food processor and blend until well combined. Then press contents through a medium mesh sieve. Whisk the butter into the liquid.
Gently beat eggs and yolk into a bowl. Slowly whisk a few spoonfuls of warm cranberry liquid into the eggs to temper, then whisk in the remainder of the eggs. Quickly clean sauce pan you just used and return liquid to the pot. Cook over low heat until the curd is nearly bubbling, about 10 minutes. Let cool to room temperature.
Pour cranberry curd into the cooled pre-baked shortbread crust and smooth top with a spatula. Bake at 350˚F for 10 minutes to set curd. Cool on a wire rack.
Store in the refrigerator. Cranberry curd will be delicious for 3 days.