Beat the butter, cream cheese and sugar until light and fluffy; scrape down the sides.
Add the milk and vanilla, and beat until incorporated, scraping down the sides of the bowl often.
Add the flour and salt and beat until combined.
Divide the dough into two discs, wrap with plastic wrap and refrigerate for at least two hours.
Remove from the fridge at least ½ hour before use.
Line 2 baking sheets with parchment paper.