Preheat oven to 425℉. In a medium bowl toss together all ingredients and spread in a single layer on a small baking sheet. Roast for 10 minutes. Remove from oven and stir, spreading out in a single layer to cool to room temperature.
Preheat oven to 350℉. Add butter to a stand mixer bowl fitted with paddle attachment and beat until smooth. Add flour, powdered sugar, cornstarch, vanilla and salt. Continue to beat until smooth and fluffy, approximately 3-4 minutes, scraping bowl and paddle down at least twice.
Scoop dough into a large pastry bag fitted with a 1M tip. Line large baking sheets with parchment and pipe dough into approximate 1 3/4"- 2" rosettes with 2" spacing. (cookie will spread slightly with cooking)
Press an approximate 1/2 tsp of roasted cranberries into centre of cookie. Top centre of cookie with course sugar and bake in centre of oven for 12-13 minutes. Remove from oven and allow to cool on baking sheet for 5 minutes. Remove to cooling rack and allow to cool completely.
You will likely have about a 1/2 cup of cooked cranberries left depending on how much you top the cookies with. Any leftover is fantastic on crostini with brie or with roasted meats.