prepare an 8x8 pan, line with foil, then grease with butter

in pan combine sugar, sour cream, salt, butter, cooking over med-high heat, stir until all is melted, cook till mixture reaches 234 (softball stage(to test for this drop a spoonful into a cup of cold water, mixture should make a softball that when taken out of the water can be flatten)) takes about 15mins

once it reaches the right temperature keep on heat and add white chocolate chips, marshmallow creme, stir till until all is mixed and smooth

remove from heat, add vanilla, working real fast here, pour half into a bowl and set aside, add root beer to remaining fudge, pour the root beer fudge in the pan, then quickly pour the white fudge over the top

working real fast take a table knife and run through fudge making a ribbon pattern, you must work fast or the fudge will become grainy and not set right

let sit for 2hrs, remove from pan and slice into squares, store in an airtight container, room temperature, for up to 1 week