Combine flour, salt, rosemary, and parmesan in the bowl of a food processor; pulse to combine.
Cut butter into tablespoon-sized slices.
Add butter; pulse until mixture resembles coarse meal.
Add 1 tablespoon of milk at a time, pulsing each time to combine.
Process until dough comes together and is well combined.
Transfer dough to a floured work surface.
Shape dough into a log. (I made mine rectangular, about 1-1/4” x 1” x 12”)
Wrap with plastic wrap, and refrigerate for at least 6 hours.
Heat oven to 325 degrees.
Line baking sheet with parchment paper.
Slice chilled log of dough into 1/4” thick slices.
Place slices on prepared baking sheet, leaving an inch between each.
Bake for 12 minutes.
Flip crackers, and bake for an additional 12 minutes or until crackers are golden brown and firm in the center.
Transfer to baking rack to cool.