In a large bowl, using mixer, cream butter, sugar on medium speed until fluffy. Add milk and vanilla, beat to combine.
With mixer on low, gradually add flour and salt, continue beating until dough forms.
Chop dried cranberries in a food processor into smaller bits. Add chopped cranberries to the dough, mix with the spatula to combine.
Divide dough into 2 portions. Shape each portion into a log. I shaped each portion into different sized logs: small and big for smaller and bigger cookies. Wrap logs in plastic wrap, put in the freezer for 30 minutes, then in refrigerator for 30 minutes.
Preheat oven to 350 F.
Place red decorating sugar on a plate. Roll each cookie log in red decorating sugar, pressing sugar to the dough to stick. Using sharp knife cut each log into thin slices, about¼ inch thick.
Place cookies on ungreased cookie sheet. Bake until edges just start turning brown, about 12 minutes. Remove from oven, place cookies to cool on wire rack.